U.S. patent number 3,672,241 [Application Number 05/060,047] was granted by the patent office on 1972-06-27 for filament rotor structures.
This patent grant is currently assigned to The Johns Hopkins University. Invention is credited to David W. Rabenhorst.
United States Patent |
3,672,241 |
Rabenhorst |
June 27, 1972 |
FILAMENT ROTOR STRUCTURES
Abstract
A rotational energy storage device comprising in its basic form
a rotor or "flywheel" structure constructed of straight anisotropic
filamentary members, the members being disposed in substantially
parallel relation to the major stress component acting on the
structure. Each filamentary member is essentially loaded along its
longitudinal axis, thereby permitting maximum utilization of high
strength-to-density uniaxial properties of the member.
Inventors: |
Rabenhorst; David W. (Silver
Spring, MD) |
Assignee: |
The Johns Hopkins University
(Baltimore, MD)
|
Family
ID: |
22026992 |
Appl.
No.: |
05/060,047 |
Filed: |
July 31, 1970 |
Current U.S.
Class: |
74/572.1;
416/230; 416/244A; 428/492; 428/902; 416/60; 416/241A; 428/114;
428/364; 428/500 |
Current CPC
Class: |
F16F
15/305 (20130101); F16C 32/0408 (20130101); F16F
15/10 (20130101); F16C 15/00 (20130101); Y02E
60/16 (20130101); Y10T 74/2117 (20150115); Y10T
428/2913 (20150115); Y10T 428/31855 (20150401); Y10T
428/31826 (20150401); Y10S 428/902 (20130101); Y10T
428/24132 (20150115); F16C 2361/55 (20130101) |
Current International
Class: |
F16C
15/00 (20060101); F16F 15/30 (20060101); F16F
15/305 (20060101); F16F 15/10 (20060101); F16c
015/00 () |
Field of
Search: |
;74/572 ;156/296,297
;161/168,172,60,239,247 ;15/179,180,181,182,186,187,188,198 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: O'Dea; William F.
Assistant Examiner: Shoemaker; F. D.
Claims
I claim:
1. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axes of said members being disposed parallel to each
other;
matrix means for bonding the members together; and,
a coating of low-vapor pressure material disposed over the surface
of the structure.
2. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, the structure comprising a
plurality of straight anisotropic filament-like members, said
members being formed into strips, the members within any given
strip being parallel, and wherein the strips are disposed within
the structure at an angle with respect to certain other strips of
parallel members.
3. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axes of said members being disposed parallel to each
other; and wherein the members are formed into a substantially
rectangular unit having a length at least ten times greater than
its width.
4. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axes of said members being disposed parallel to each
other;
and wherein the members are formed substantially into a cylindrical
unit of a length at least ten times greater than its diameter.
5. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axes of said members being disposed parallel to each
other;
and wherein said structure has a symmetrical cross-sectional
profile defined by opposed surfaces about the axis or rotation,
said structure having a relatively thick center portion around said
axis and relatively thin end portions, said surfaces of said
profile each having the shape of an exponential curve and being
symmetrical about a plane extending through the geometrical center
of the structure and perpendicular to the axis of rotation.
6. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axis of said members being disposed parallel to each
other;
and wherein said structure is symmetrically contoured in
cross-section about said axis of rotation and has a center portion
of maximum thickness around said axis and end portions of minimum
thickness at the end portions,
the center portion of the structure having a cross-sectional
thickness diminishing non-uniformly from said maximum to said
minimum according to the relation:
y = y.sub.o e.sup.-.sup.kx
wherein:
y.sub.o = one-half of the thickness of the structure at the axis of
rotation
y = one-half of the thickness of the structure at any point on the
surface of the structure
e = the base of the natural system of logarithms
x = a spinning radius of a point on the surface of the
structure
k = a numerical constant.
7. The energy storage structure of claim 6 wherein k is in the
range of numerical values between 2.5 and 100.
8. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, comprising,
a plurality of straight anisotropic filament-like members, the
longitudinal axes of said members being disposed parallel to each
other; and wherein each member is shaped according to the
relation:
y = y.sub.o e.sup.-.sup.kx
wherein:
y.sub.o = one-half of the thickness of the structure at the axis of
rotation
y = one-half of the thickness of the structure at any point on the
surface of the structure
e = the base of the natural system of logarithms
x = a spinning radius of a point on the surface of the
structure
k = a numerical constant.
9. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, the structure comprising a
plurality of initially straight anisotropic filament-like members
having maximum strength-to-density along their longitudinal axes,
said members being oriented within said structure with the
longitudinal axis of each member disposed substantially parallel to
the longitudinal axis of the structure, said structure further
comprising,
hub means for holding the members at their centers of rotation,
rotation of the structure causing the members to fan out, each said
member aligning substantially along the local principal stress
vector acting thereon.
10. The energy storage structure of claim 9 wherein the members are
initially formed substantially into a rectangular unit having a
length at least ten times greater than its width.
11. The energy storage structure of claim 9 wherein the members are
initially formed substantially into a cylindrical unit having a
longitudinal dimension at least 10 times greater than its
diameter.
12. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, the structure comprising a
plurality of anisotropic filament-like members, said members being
formed into strips, the members within any given strip being
parallel, and wherein the strips are formed into a generally disc
shape comprising two opposing surfaces and a circular peripheral
edge, the structure being symmetrically contoured in cross-section
about said axis of rotation, and having a center portion of maximum
thickness and edge portions of minimum thickness.
13. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, the structure comprising a
plurality of anisotropic filament-like members, the structure being
formed into a generally disc shape,
a multiplicity of the members being bonded together into flat
strips and having the longitudinal axis of each member oriented
therein substantially parallel to adjacent members,
the strips further extending through and perpendicular to the axis
of rotation and being bonded together in a regularly offset angular
relation to each other whereby each strip contacts at least one
other strip on at least one of its surfaces.
14. The energy storage structure of claim 13 wherein adjacent
strips are maintained in contacting relation with each other over
major portions of their surfaces.
15. An energy storage structure rotatable about an axis of rotation
extending transversely therethrough, the structure comprising a
plurality of essentially anisotropic filament-like members having
maximum strength-to-density along their longitudinal axes,
the members being bonded together into a plurality of essentially
flat strips and having the longitudinal axis of each member
oriented therein substantially parallel to the longitudinal axis of
the strip, the strips extending through and perpendicular to the
axis of rotation and progressively and successively surmounting
each other and being built-up and bonded together in a regularly
offset angular relation to each other with certain of said strips
extending in a counterclockwise direction and certain other of said
strips extending in a clockwise direction.
16. In an energy storage system
a rotatable shaft,
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 axis
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.
17. The energy storage system of claim 16 wherein the filament-like
members are oriented within the energy storage structure with the
longitudinal axis of each said member disposed along a principal
stress vector acting on the filament during rotation of the
structure.
18. An energy storage structure rotatable about an axis extending
transversely therethrough, comprising,
a multiplicity of anisotropic filaments having maximum
strength-to-density along their respective longitudinal axes, the
filaments being oriented within said structure with the
longitudinal axis of each said filament disposed along the vector
summation of the principal forces acting on the filament during
rotation of the structure.
19. The energy storage structure recited in claim 18, including
means engaging the structure at its midpoint and mounting said
structure for rotation about said axis.
20. In an energy storage system,
a shaft rotatable around a stationary axis, and
a plurality of energy storage rotary structures mounted on the
shaft, and having axes of rotation coincident with the axis of
rotation of the shaft when the longitudinal axes of respective
cross-sections taken through the structures are perpendicular to
the shaft,
each of said structures comprising a plurality of straight,
filament-like members, said members being oriented within each
structure with their longitudinal axes disposed substantially
parallel to the longitudinal axis of a section of the rotary
structure taken parallel to the member.
21. The energy storage system of claim 20 and further
comprising
hub means on each of the rotary structures, and pin gimballing
means on each of said hub means,
the shaft having a plurality of ports for receiving one each of
said rotary structures therethrough and a plurality of recesses
perpendicular to, aligned with and communicating with each of said
ports for receiving said pin gimballing means, the rotary
structures being capable of pivotal displacement around said
gimballing means to relieve precessional loading on the shaft.
22. 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 axis
of a cross-section taken through the structure is perpendicular to
the shaft,
said structure comprising a plurality of anisotropic filament-like
members oriented with their longitudinal axes parallel to each
other.
23. The energy storage system of claim 22 and further
comprising,
internal hub means on the said structure,
pin gimbaling means on said internal hub means, and
external hub means formed with the shaft for receiving the energy
storage structure therethrough, said external hub means having
recesses therein for receiving said pin gimballing means, the
energy storage structure being capable of pivotal displacement
around said gimballing means to relieve precessional loading on the
shaft.
24. The energy storage system of claim 23 and further comprising an
elastic sleeve disposed around the said structure and between said
structure and said internal hub means.
25. An energy storage structure comprising a plurality of
anisotropic filament-like members rotatable about an axis extending
transversely therethrough,
said structure having a generally wedge-like cross-section with
wedge-shaped leading and trailing surfaces,
the structure being symmetrical about a plane extending through the
geometrical center of said structure perpendicular to the axis of
rotation.
26. An energy storage structure rotatable about an axis extending
transversely therethrough, comprising,
a plurality of anisotropic filament-like members arranged with
their longitudinal axes parallel, and
hub means including arcuately shaped spaced walls,
said hub means engaging said members with the mid-portions of said
walls in engagement with the mid-portions of said members,
the members fanning out on rotation of the structure whereby the
portions of said members within said hub means will bear against
said walls and be supported thereby.
Description
The invention herein described was made in the course of or under a
contract or subcontract thereunder, with the Department of the
Navy.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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
powered portable hand tools.
2. 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 bursting limit. In the
prior art, three general flywheel configurations are predominant,
namely, the flat disc type characterized by smooth parallel
surfaces between the hub and the periphery; the rim type having a
massive peripheral portion secured to the hub by spokes or a solid
wheel portion; and the more recently developed optimized disc.
Materials used to fabricate high-energy flywheels must have large
specific strengths (strength/density) to enable the structure to be
rotated at a high velocity. High strength steel has ordinarily been
chosen as flywheel material. However, the strength/density ratio of
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.
The present rotational energy storage device features flywheel
rotor structures capable of substantial improvement in useable
energy density, primarily because a much higher percentage of
filament specific strength is useable. Characteristic of the
present rotor structure is the use of straight anisotropic
filamentary material arranged in the structure so as to permit
maximum utilization of the filament strength in its axial
direction.
The significance of the present energy storage device is best
understood by its application to the urban vehicle. Although
flywheels have been previously used in short-range vehicles, such
as in the Swiss Oerlikon bus and in the British Gyreacta
transmission, these devices produced only about 3 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 to storage 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, the flywheel can
be charged at any reasonable rate. Thirdly, the flywheel 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 capability of 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 source in an urban vehicle.
SUMMARY OF THE INVENTION
The invention primarily concerns a number of rotor structural
configurations which form the major component of a high performance
energy storage device. The several rotor configurations actually
described herein, and those other configurations which follow from
the description, are related in their use of high strength uniaxial
filament-like materials to comprise the rotor structure. In
particular, straight anisotropic filament or "whisker" materials
are not only disposed substantially parallel to each other over the
entire length of the rotor but are also substantially parallel to
the major stress component acting on the rotor. Like any other
flywheel device, the performances of the present rotor
configurations are directly proportional to the specific strength
of the material used in construction. By taking maximum advantage
of the large specific strengths of filamentary materials, i.e., by
aligning these filamentary materials substantially parallel to each
other and 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.
In the straight filament rotor configurations disclosed herein the
low stresses which exist normal to the filaments are supported by a
suitable matrix material or by a combination of a relatively few
added filaments disposed normal to the principal filaments and
potted in a suitable matrix material. For certain applications
using high strength continuous filaments, such as ordinary music
wire or boron filaments, a matrix is not required to maintain the
filaments in alignment. In such a device, the filament bundle is
secured in a central hub, which, when rotated, causes the filaments
to fan out and align along respective force vectors generated by
their own rotating masses. In such a configuration virtually all of
the available strength of the material is effectively used at the
maximum stress point (center of rotation).
In order to accommodate the extremely high rotational speeds of
which the present device is capable, the performance limits of the
bearings which support the rotating shaft must be maximized.
Additionally, the rotating member must be maintained in a vacuum to
reduce aerodynamic drag losses, thus presenting the necessity for a
high-speed rotary seal or a passive magnetic coupling to drive the
rotor through the wall of the vacuum chamber. Bearing and sealing
functions can be provided through use of a combination of magnetic
fluid seals, magnets, and bearings which allow operation of the
rotating member under these conditions.
Accordingly, it is a primary object of the invention to provide a
high power-density energy storage device which also has a high
energy density capability.
It is another object of the invention to provide rotary structures
capable of higher rotative speeds for higher energy outputs than
have been previously available.
It is a further object of the invention to provide a rotor
structure comprising substantially parallel high strength
filamentary materials aligned along the major stress component
acting on the structure.
Yet another object of the invention is to provide an energy storage
device capable of operating at an abnormally high rotation speed
with minimal aerodynamic and bearing drag losses.
A further object of the invention is to provide an energy storage
device which can be readily and efficiently made from a large
number of small autonomous rod-like components to minimize the
likelihood of simultaneous failure of all components, thus
maximizing the safety of the device.
It is also an object of the invention to provide a rotor structure
having inherent gimballing capability about a stationary spin axis
to minimize gyroscopic loads on the rotor and its spin
bearings.
A still further object of the invention is to provide a safe,
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
FIGS. 1a, b, and c are enlarged perspective views of the sequential
build-up of an embodiment of the invention, FIG. 1a showing a
single, essentially uniaxial filament which forms the basic unit of
the uniaxial strip of FIG. 1b, which strip in turn comprises the
secondary structural unit of the composite bar of FIG. 1c;
FIG. 2 is a perspective of a "bar" rotor fabricated according to
the invention;
FIG. 3 is a plan view of a rotating "brush" rotor fabricated
according to the invention, the rotor being shown with filaments
aligned along local stress vectors, the unspinning rotor being
shown in phantom;
FIG. 4 is a schematic illustrating the fanning load operating on a
point on a filament in a rotor constructed according to the
invention;
FIG. 5a is a perspective of an optimized bar rotor fitted with an
internal gimbal, a portion of the rotor being cut away to
illustrate the increasing length of the filaments which are shown
to be enlarged in the cut-away portion;
FIG. 5b is a cross section taken through the geometrical and mass
center of the embodiment of the invention shown in FIG. 5a;
FIG. 6 is a section taken longitudinally through the optimized bar
rotor shown in perspective in FIG. 5a;
FIG. 7a is an elevation of a disc rotor constructed according to
the invention;
FIG. 7b is a plan view of the disc rotor of FIG. 7a;
FIGS. 8a and 8b are perspectives of "wedge" rotors fabricated
according to the invention, the rotor of FIG. 8b being fitted with
a hub conforming to the cross sectional dimensions of said
rotor;
FIGS. 9a, 9b, 9c, and 9d are schematics illustrating the relative
drag of wedge rotors having varying half-angles as compared to the
square block shown in FIG. 9a;
FIG. 10 is a partial section of an energy storage system useful
with the present invention and having bearings within an associated
vacuum can;
FIG. 11 is a perspective of a magnetic coupling device useful with
the system shown in FIG. 10;
FIG. 12 is a partial section of an energy storage system useful
with the present invention and having magnetic liquid seals which
allow use of bearings disposed externally of an associated vacuum
can;
FIG. 13 is a cross-section of a magnetic fluid bearing useful to
prolong the charged life of the present invention;
FIG. 14 is a perspective of an internally gimballed multiple rotor
energy storage device structured according to the invention;
and,
FIGS. 15a and 15b are elevations of a portion of the device of FIG.
14, the device being shown in a precessed mode in FIG. 15b.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The performance, i.e., the stored kinetic energy of a rotating
body, is directly proportional to the useable specific strength of
the material used in the fabrication of the body.
Prior flywheels of optimum configuration composed of isotropic
material such as solid steel have only a small fraction of useable
strength to density compared with modern filamentary materials. A
common uniaxial filamentary material, fine high-grade music wire,
while not the most advantageous material for fabrication of the
present rotor structure, has a useable specific strength of
1,500,000 lbs-in/lb, or about three times that of solid steel. A
flywheel rotor configured to take maximum advantage of the
anisotropic strength characteristics of uniaxial filamentary or
whisker materials is capable of increased performance relative to
flywheels composed of isotropic materials.
The term "anisotropic" is generally defined as exhibiting
properties with differing values when measured along axes taken in
different directions. For the purposes of this disclosure,
"anisotropic" is applied to a material to denote the property of
strength along axes taken in different direction within the
material. In particular, the term relates to a material having
maximum strength along one particular axis thereof. For the
filamentary materials or thin rods used in the present rotor
structures, the axis of the material along which said material has
maximum strength is the longitudinal axis of the material.
Considering the single filament or thin rod 10 shown in FIG. 1a to
be spinning about its major axis, the specific energy of the
filament 10 is given by:
E.sub.sp = 32.2 I S A/W.sup.2 R (1)
where:
E.sub.sp = specific energy: foot-pounds per pound
I = moment of inertia: slug-ft.sup.2
S = allowable stress: lb/in.sup.2
A = rod cross section: in.sup.2
W = weight: lb
R = one-half the spinning radius: ft
or,
E.sub.sp = 32.2 (IA/WR) (S/W) (2)
As is the case with prior art flywheels composed of isotropic
materials, it is apparent from Equation (2) that the specific
energy of the filament 10 is also a function of the specific
strength (S/W) of the filament material. Similarly, the actual
energy storage capability of a flywheel rotary device is given by
Equation (1).
If the diameter of the filament 10 is infinitely small, the total
stress in the filament is directed along its length, i.e., the
direction of the centrifugal force acting on the filament 10,
which, for the situation described, is the only force acting on the
filament during rotation. If the filament 10 were the only element
in a flywheel or rotating member, all of its allowable strength at
its center contributes to the kinetic energy of this single element
flywheel. If the effective shape of the filament 10 were optimized
according to the principles described hereinafter for total rotor
optimization, performance of the single filament rotor would be
substantially increased.
In practice, the single filament 10 would have insufficient mass
for most energy storage applications. However, FIGS. 1b and 1c
illustrate the build-up of a flywheel rotary member according to
the present invention. In FIG. 1b, a plurality of single filaments
10 are aligned substantially parallel to each other to form a
layered unidirectional strip 12. The width of the strip 12 is held
to a low proportion of its length, such as 1:10 or 1:20 in order to
minimize that force which acts to spread the filaments 10 apart due
to the impossibility of aligning each filament 10 along the
centrifugal force vector acting on the strip 12. Referring briefly
to FIG. 4, the magnitude of the fanning load, L.sub.f, at a point P
on a filament 10 will be
L.sub.f = SR sin .alpha. (3)
where S is the operating filament stress, R is the spinning radius
of the point P where the fanning load is being determined, and
.alpha. is the angle between the centerline of the strip 12 and a
line connecting the center of rotation and the point of interest.
Since sin .alpha. = h/R, Equation (3) can be written:
L.sub.f = SR h/R (4)
or
L.sub.f = Sh (5)
Thus, the magnitude of the fanning load on a given filament on the
spinning strip 12 will be the same at any point on the
filament.
The strips 12 are stacked to form a rotor bar 14 of a desired total
weight and potential performance shown in FIG. 1c. The filaments 10
in the rotor bar 14 may be bonded together by a matrix 15 such as
silicone rubber, epoxy, metal or a plastic or elastomeric material.
The bar 14 in FIG. 1c is shown in the simple shape of a rectangular
solid, although the bar shape may be optimized to provide greater
energy storage capability, as will be described hereinafter.
Optimization of the shape of each filament 10 according to the
principles described for optimization of the total bar rotor would
yield increased performance but at a substantial increase in
production cost and effort.
Referring to FIG. 2, a "bar" rotor 20 fabricated in essentially
that fashion indicated for the bar 14 of FIG. 1c is shown.
Straight, parallel, essentially uniaxial filaments 10 are bonded
together in a matrix 22 of metal, plastic, or elastomeric material
capable of supporting the fanning loads generated by the rotating
mass of each filament 10. The matrix 22 may also bond to the rotor
20 one or more layers 24 of filaments having their axes disposed
normal to the filaments 10. These layers 24 could be only one
filament thick and could be regularly disposed throughout the rotor
20 to give additional resistance to fanning load stressing.
However, the ratio of filaments in the layers 24 must remain low
relative to the number of filaments 10 in order to maximize the
useable strength of the filament material. The rotor 20 consisting
of bonded filaments 10 in the simplified form of a rectangular
solid is bonded within a rectangular, sleeve-like hub 26 composed
of steel or other high strength material. The hub 26 has an
integral shaft 28 comprised of upper and lower shaft members 30
which extend normal to and from the upper and lower major plane
surfaces 32 of the hub 26, which surfaces 32 are substantially
parallel to the filaments 10. The rotor 20 may be additionally
secured within the hub 26 by means of an epoxy-type adhesive or by
a high strength filler compound such as those materials used to
form the matrix 22. On rotation of the "bar" rotor 20, the
principal load, F, on the rotor 20 is aligned along the
longitudinal axis of the rotor, i.e., along and parallel to the
filaments 10. Rotor spin-up and power takeoff is accomplished in a
known fashion through the hub 26 and associated shaft 28. The use
of certain continuous filamentary materials, such as music wire,
boron filaments, etc., to form the rotor bar 14 do not require a
matrix to maintain the filaments 10 in operative disposition. As
shown in the "brush" rotor 16 in FIG. 3, the filaments 10a are
allowed to fan out and align themselves with the local centrifugal
force vector acting on each filament. As shown in phantom in FIG.
3, the loose filaments 10a are clamped together substantially
tangentially between two rounded abutments 19 which form walls of a
hub 18, which internally rounded walls are substantially parallel
to the axis of rotation of the rotor 16. The filaments 10a remain
substantially parallel in a bar shape until rotation commences. On
rotation of the rotor 16, the filaments 10a fan out symmetrically
around the longitudinal axis of the rotor and line up precisely
with the respective force vectors generated by their own rotating
masses. The filaments 10a contacting that small portion of the
perimeter of the abutments 19 holding the filaments when the rotor
is at rest, fan out and virtually impress themselves against the
full length of the perimeter of the abutments 19, i.e., assuming
the shape of the abutments to be advantageously formed to
approximate the shape assumed by the filaments under the operating
conditions. The hub 18 could alternatively be cylindrical rather
than the external rectangular solid shown in FIG. 3. In either
event, the length of the hub 18, i.e., that dimension parallel to
the longitudinal axis of the rotor 16, should be at least twice as
great as the width or diameter of the hub. The strength
degeneration of the filaments 10a caused by the moderate bending of
each filament as it passes through the hub 18 is negligible.
If music wire filaments having a useable specific strength of
1,500,000 lbs/in.sup.2 are utilized in the "brush" rotor 16, the
energy storage capability is nearly twice that of a disc flywheel
of optimized shape and constructed of isotropic steel such as is
disclosed by Call in U.S. Pat. No. 3,496,799. The energy storage
capability of the "brush" rotor, though greater than the
capabilities of previous flywheels, would be less than that of a
theoretically optimized anisotropic disc due to the difference in
effectiveness of the two configurations. A practical optimized disc
configuration using anisotropic material will also be described
hereinafter.
The actual energy storage capability of the "brush" rotor 16 and of
the simple "bar" rotor 20 of FIG. 2 is given by Equation (1). By
substituting appropriate values in Equation (1), it is seen that
the "brush" rotor 16 is capable of storing at least 16 watt-hours
per pound, taking the usable strength of music wire to be about 70
percent of the tensile strength of the material (600,000
lbs/in.sup.2). Such a value would apply to mechanical energy
storage systems not subject to personnel hazard restrictions nor
exposed to more than a few thousand cycles of operation. Since
factors other than specific strength of a material govern the
specific energy content of a particular rotor configuration, the
usable strength of a material will not always be the same
proportion of the specific strength for all materials. If the "bar"
rotor 20 were constructed of laminated high strength glass
filaments and if appropriate allowances were made for personnel
safety factors, handling degradation, static fatigue, cyclic
fatigue, filament volume, and filament alignment, then the
allowable strength could be as low as 25 percent of the tensile
strength of the material. Even so, the glass filament "bar" rotor
20 would still have twice the specific energy capability of the
music wire "brush" rotor 16 by virtue of its greater specific
strength at the design condition.
The performance of the "bar" rotor 20 may be optimized in a fashion
illustrated in FIGS. 5a and 6 so that the major stress component
acting on the rotor is constant along its length. As seen in the
drawings and particularly in the sectional view of FIG. 6, an
optimized bar 34 has oppositely facing surfaces 35 and 37 defined
by respective lines of rotation having an effective radius L and
which are substantially mirror images across a longitudinal
centerline of the bar 34. The surfaces 35 and 37 produced by the
lines of rotation are characterized by a generally reverse
curvature in the cross-sectional profile seen in FIG. 6, the
surfaces being essentially convex near the center of rotation 39 of
the bar 34 and sloping to a substantially concave shape near the
ends 36 of the bar. Thus, the shape of the bar 34 is seen to
generally decrease in thickness from a maximum at and around the
center of rotation 39 to a minimum at the ends 36 of the bar. To
achieve maximum rotor optimization, the thickness of the ends 36
would continuously diminish to infinity, thus practically producing
a razor sharp edge. Practical considerations dictate forming the
ends of the bar into a substantially square cut edge such as is
shown at 41 in FIG. 6.
Generally, constant stressing of the bar is approximated when the
cross-sectional thickness of the bar diminishes non-uniformly from
a maximum thickness to a minimum thickness according to the
relation
y = y.sub.o e.sup.-.sup.kx (6)
where
y.sub.o = one-half of the bar thickness at its center of
rotation,
y = one-half of the bar thickness at any point on the surface of
the bar,
e = the base of the natural system of logarithms, i.e.,
2.71828...
x = the spinning radius of the point
k = a numerical constant for a particular configuration Equation
(6) yields a family of coordinates which explicitly defines the
cross-sectional profile of the rotor 34 best shown in FIG. 6. The
constant, k, in Equation (6) may be any real number. However,
values of k greater than 100 or less than 2.5 yield impractical
rotor configurations. The rotor shaping yielded by Equation (6) can
be practically approximated by either two cones joined at their
bases and symmetrical across the axis of rotation or two regular
pyramids joined at their bases (not shown). The rotor 34 could
alternatively be shaped according to Equation (6) but having square
or circular axial cross-sections at any distance from the axis of
rotation of the rotor.
This optimized bar 34 will yield at least 50 percent greater
performance than the bar rotor 20 described previously. The rotor
34 may be initially formed as a rectangular solid with straight,
parallel filaments in the manner of the "bar" rotor 20 of FIG. 2.
However, the rectangular bar is machined to the shape shown in
FIGS. 5a and 6, thereby causing the filaments to have increasing
length as is illustrated by enlarged filaments 10s shown in a
cut-away portion of the rotor 34. The maximum load on the shorter
filaments 10s at and near the center of rotation of the optimized
bar 34 is distributed over a greater number of filaments which are
not as heavily loaded as the full length filaments 10e shown
enlarged at the ends of the rotor 34. Stated in another fashion,
the short filaments 10s act to increase the load carrying
capability of the longer center filaments 10e through additional
shear load in the matrix. If each filament 10s and 10e of the rotor
34 were optimized in shape according to Equation (6), maximum
performance optimization would be obtained.
The optimized bar 34 pictured in FIGS. 5a, 5b, and 6 also serves to
illustrate an internal gimbal arrangement, shown generally at 38 in
FIG. 5a and in section in FIG. 5b, which minimizes gyroscopic
precession loads on the bearings used to hold the shaft supporting
the bar 34 and on the rotating bar. In the bar configuration, the
internal gimbal arrangement 38 described avoids the necessity for
otherwise having large external gimbal rings and their associated
bearings. More importantly, the rotor shaft does not have to be
gimballed, enabling its output to be used directly. The gimbal
arrangement 38 is seen to comprise a hollow box-like internal hub
40 which generally, assumes the shape of the rotor cross-section.
The hub 40 is preferably constructed of steel or other high
strength material. The optimized bar 34 is centered within the hub
40 and held therein by means of an elastic sleeve 42 disposed over
that portion of the bar's surface held within the hub. The elastic
sleeve 42 is contiguous to the bar 34 on the inner surfaces of the
sleeve and contiguous to the inner surfaces of the hub 40 on the
outer surfaces of the sleeve to form a tight fitting within the hub
40. The sleeve 42 is made of elastic material in order to effect a
better fit within the hub without inducing local stress
concentrations. The sleeve 42 could well be fabricated from
non-elastic material if this protection were not required in a
particular application. As can be better seen in the sectional view
in FIG. 5b, the hub 40 has two gimbal pins 44 extending from its
opposite vertical faces, the pins 44 being aligned through the mass
(and geometrical) center of the bar and hub combination. The pins
44 can be formed integrally with the hub 40 for increased
structural strength.
A hollow box-like external hub 46 having four rectangular faces
mountably encloses the bar 34 and hub 40 combination described
above. The external hub 46 has two cylindrical recesses 48 disposed
in and centered on its opposite vertical faces for receiving the
gimbal pins 44. The pins 44 extend into the recesses 48 a
sufficient distance to provide positive gimbal mounting of the bar
34 and hub 40 combination within the external hub 46. Anti-friction
or elastomeric bearings (not shown) can be fitted into the recesses
48, if required. Stud shafts 50 extend from the opposite horizontal
faces of the hub 46 and are aligned through the mass (and
geometrical) center thereof. The hub 46 and shafts 50 are formed
integrally with the hub and are made of steel or other easily
worked high strength material. The gimbal limits of the bar 34 are
determined primarily by the relative dimensions of said bar 34 and
the external hub 46, particularly the clearance provided between
the bar and hub and the length of the horizontal faces of the hub.
For any foreseeable vehicle application wherein the flywheel is
disposed therein with a vertical spin axis, reasonable gimbal
limits are easily provided by the arrangement 38. The gimbal
arrangement 38 is easily adapted to the "brush" and gimballing
rotor 16 of FIG. 3 and to the "bar" rotor 20 of FIG. 2. Geometrical
modification of the internal and external hubs 40 and 46 allows
shaft attachment to and gimballing of the various rotor shapes and
configurations which can be fabricated according to the
invention.
The optimized bar 34, although capable of high energy storage
capacity, is subject to aerodynamic drag losses directly
proportional to the pressure and gas density within the vacuum can
in which it is being rotated. For any given partial vacuum now
practically maintainable (.apprxeq.10.sup.-.sup.4 torr), it can be
shown that a disc shaped rotary member reduces drag losses by at
least one order of magnitude, i.e., compared to a straight bar
configuration having essentially the same diameter, volume, weight
and rotary speed. The drag of the optimized bar is also about three
times less than the straight bar, but must be operated at a higher
speed to achieve its greater performance. Additionally, the volume
of the vacuum can enclosing the disc-type rotor is substantially
smaller than is possible for a non-optimized bar rotor.
A "disc" rotor 52 fabricated according to the present invention is
shown in FIGS. 7a and 7b. The shape of the "disc" rotor 52 is
coincidentally similar to that disclosed by Call in U.S. Pat. No.
3,496,799. Call provides a disc flywheel composed of isotropic
material with an optimized generally lenticular shape which
produces a substantially uniform stress throughout the flywheel
mass during rotation.
The "disc" rotor 52 is seen to progressively decrease in thickness
from a maximum at and around the hub or center of rotation 54 to a
minimum at the circumferential tip 60. This configuration is built
up by bonding together a plurality of the unidirectional strips 12
previously shown in FIG. 1b.
The strips 12 are stacked in an offset sequence, the geometrical
center of each rectangular strip 12 being coincident with the
center of rotation 54 of the rotor 52. The strips 12 may be
initially stacked into a rectangular solid with the four edges of
each strip 12 being aligned with the edges of the other strips 12,
the resulting structure then being "fanned out" by offsetting each
said strip 12 a finite angular distance from the immediately
adjacent strips 12. By continuing the relative angular offset of
adjacent strips 12 around a full 360.degree. angle, the geometrical
relationship shown in FIG. 7b is produced. The strips 12 are then
bonded into a matrix to maintain them at the proper angular offset.
As an idealized and simplified example, if the rotor 52 were
comprised of twelve of the strips 12, then each strip 12 would be
"fanned out" from the aligned rectangular solid described above at
an angle of 30.degree. relative to the adjacent strips 12 in the
rotor 52, thereby forming a disc-shaped member having maximum
thickness at or around the center of rotation 54 and minimum
thickness at the circumferential tip 60. At the center of rotation
54 the thickness of the rotor 52 is comprised of a finite
contribution from each of the strips 12 comprising the rotor. At
the circumferential tip 60, the thickness is comprised of the
finite contribution of a relatively smaller portion of the strips
12, thereby yielding a differential thickness which results in the
generally lenticular shape shown in FIG. 7a. The filaments
comprising the strips 12 are substantially aligned within the rotor
52 with the local centrifugal force vector acting on each filament,
thereby providing an energy storage capacity consistent with the
maximum useable specific strength of the filaments themselves. Hub
mounting means (not shown) for power takeoff and flywheel spin-up
may be provided by bonding metal hubs to either side of the hub or
center of rotation 54.
A bi-directional fanning of the strips 12 produces a "wedge" rotor
62 shown in FIG. 8a. The aerodynamic drag on the rotor 62 can be
shown to be about equal to the drag acting on the optimized "disc"
rotor 52. However, the advantage of the wedge configuration is that
its straighter filaments are more nearly lined up with the radial
force vector. Although a vacuum can surrounding the "disc" rotor 52
can be made smaller than that required for the "wedge" rotor 62,
all of the uniaxial filaments comprising the "wedge" rotor can be
straight and aligned virtually parallel to the local centrifugal
stress vector acting on each filament. The "wedge" rotor 62 is seen
to result from a buildup of the unidirectional strips 12, one of
the strips 12 being at first slightly and regularly offset relative
to the next lower strip 12 in a counterclockwise direction, and the
strip build-up then being reversed to a clockwise direction.
Aerodynamic drag acting on the "wedge" rotor 62 depends on the
slope of the surface of the strips 12, i.e., the magnitude of the
relative offset between said strips 12. This factor is more easily
discussed by consideration of the half-angle between the line
defining the fanning surface and a line normal to the axis of
rotation through the wedge caused by the reversal in strip buildup.
As seen in FIGS. 9a, 9b, 9c, and 9d, drag varies significantly in
proportion to the half-angles shown taken through the
cross-sections of several representative wedge shapes. Assuming the
rectangular body 64 of FIG. 9a to have a normalized drag of 100
percent, the "wedge" rotor of FIG. 9b, having a half-angle of
14.degree.29', exhibits a relative drag of 10.5 percent.
Progression to lower half-angles produces reduced drag, but
eventually produces dimension problems of greater severity, since
the filaments tend to separate tangentially when elongated under
the radial stress vector.
FIG. 8b illustrates a "wedge" rotor 62a having a hub 40a shaped to
accommodate the wedge shape of the rotor in the manner indicated
hereinabove.
For purposes of illustration, FIG. 10 shows a state-of-the art
energy storage system 65 capable of use with the present energy
storage device. The "disc" rotor 52 is shown in this view as the
energy storage device, but, with alteration of the shape of certain
components of the system 65, any configuration of the present
energy storage device may be used in the system. The system 65
comprises a hermetically sealed vacuum can 66 which generally
follows the shape of the rotor 52 except near the axis of rotation
68 of said rotor where the can 66 is provided with integral
cylindrical extensions 70 and 72. The extensions 70 and 72 both
accommodate dry bearings 74 and respectively accommodate a plate
76a of a magnetic coupler 76 and a magnetic suspension device 78.
The bearings 74 are burnished with MoS.sub.2 or other suitable dry
lubricant, and function without additional lubrication in the
vacuum environment within the can 66. The dry bearings 74 are
completely unloaded for the static situation by the permanent
magnetic suspension device 78 and are only loaded in a dynamic
operating environment, such as in a vehicle. Low vapor pressure
lubricating oils can also be used at these modest vacuum pressures.
However, if the system 65 is installed in a vehicle with the spin
axis vertical, then x and y axis gimbals 80 and 82 act to relieve
gyroscopic precessional loads caused by pitching and turning of the
vehicle. Operation of the flywheel with the system 65 thus disposed
does not effect vehicle turning, nor does vehicle turning affect
the flywheel, since the vehicle turns around the spin axis of the
rotor 52.
The rotor 52 is mounted on a two-piece shaft 84 coinciding with the
spin axis of the rotor. The shaft 84 is journaled at each end in
the bearings 74 and terminates at its upper end at the plate 76a of
the magnetic coupler 76 and at its lower end at permanent magnet
78a of the magnetic suspension device 78. Plate 76b of the magnetic
coupler 76 is disposed outside of the vacuum can 66, the plate 76b
being driven in this instance by an electric motor 86, said plate
76b, in turn, driving the plate 76a which spins the rotor 54
without direct connection through a non-magnetic portion of the
vacuum can 66. By utilizing such an indirect drive system, high
speed rotating seals are not required; thus the operating pressure
inside the vacuum can may be held lower than might otherwise be
possible.
The magnetic coupler 76 is shown in greater detail in FIG. 11. The
coupler 76 comprises the two plates 76a and 76b which each consist
of a multipole magnet 88 and an iron backing 90, the backing 90 of
the plate 76a being attached to the shaft 84 and the backing 90 of
the plate 76b being joined to a shaft member 92 coupled to the
electric motor 86. The present energy storage device, because of
its high speed and low torque characteristics, is especially suited
for use with the coupler 76. Since the magnetic coupler 76 is not
novel and is well-known in the art, further description thereof is
not given herein. However, it should be noted that, despite the
advantages of a hermetically sealed vacuum can and the improved
vacuum condition thus made possible, the coupler 76 has the
relative disadvantage of losing lock between the plates 76a and 76b
if design torque is exceeded, and will not relock without a full
restart.
Returning to FIG. 10 and the system 65 the vacuum can 66 is
provided with a safety ring 94 and a gimbal frame 96. A shock
absorbing suspension 98 stabilizes the system 65. If the internal
gimballing arrangement 38 of FIGS. 5 and 6 is used with an aptly
sized vacuum can, the external gimbals 80 and 82 may not prove
necessary for most applications. In the system shown, compensation
for precession resulting from the earth's rotation can be provided
either in the form of springs, slight friction, or by locating the
gimbal axes slightly above the swung center of gravity, so that the
system 65 will be self-compensating.
Spin-up of the rotor 52 is accomplished as described previously.
Power take-off is similarly accomplished. In this instance, the
electric motor 86 becomes a generator converting mechanical energy
to electrical energy for efficient conduction to electric motors,
such as at the wheels of a vehicle. Power take-off can just as
easily be accomplished by means of hydraulic motors and pumps, or
an all mechanical system could also serve in place of the electric
motor 86.
Certain applications are better accomplished by using a turbine or
internal combustion engine (with an over-riding clutch) as the
driving motor. In the hybrid installations the engines could be
much smaller than usual, since the flywheel would provide all of
the extra power required for acceleration of the vehicle. Using the
instant concept, the flywheel in such a hybrid vehicle would only
weigh about 1 percent of the vehicle weight. At a can pressure of
10.sup.-.sup.4 torr, the rotor 54 could be run for several days
despite bearing losses. By comparison, the useable power for the
flywheel used in the Oerlikon bus was diminished in a few
hours.
The safety hazard of the present energy storage device is minimized
relative to conventional flywheels since the present structure
comprises a large number of relatively small highly stressed
components. A rotor having a total energy content of 25,000,000
ft-lbs, would constitute a formidable hazard if it were fabricated
of a single piece of isotropic material and were to fail at the
rated speed. However, fabrication of the present rotor 52 from
music wire strands 0.003 inch in diameter would result in a kinetic
energy on a single strand of wire of only 1 to 2 ft-lbs. In any
conceivable rotor configuration, the matrix strength will be only a
small percentage of the strength of the filamentary material, thus
resulting in a relatively progressive failure, rather than the
instantaneous failure occuring with single-piece flywheels.
The high rate of rotation possible with the present energy storage
device results in low torque, since the torque varies indirectly
with the rotation speed of the flywheel for a given power level.
For example, an embodiment of the present energy storage device
capable of producing 50 horsepower at 35,000 rpm would exert a
torque of only 7.5 ft-lbs. For the music wire rotor 52 described
above, the torque exerted on each wire would be only 3 .times.
10.sup.-.sup.7 ft-lbs. The low torque would have a negligible
effect on the rotor as well as on a vehicle in which the rotor
could be used.
The most significant factor governing the performance of the
present energy storage device is the usable specific strength of
the filamentary or whisker material used in its construction.
Presently available wire material is in almost every instance
stronger along its length than the parent material in bulk form.
Steel wire is available having a tensile strength of 600,000
lbs/in.sup.2. Other wire material, such as beryllium wire, actually
exceeds the specific strength of steel wire. More exotic
filamentary and whisker material now available includes fiberglass,
graphite, boron, tungsten-carbide, etc. These available materials
have been developed because of the need for high strength, high
temperature, and, usually, lightweight materials. However, the
present use requires only the high specific strength
characteristic, since the high temperature capability is not
required.
Most filamentary and whisker materials described, unlike the wire
materials, must be bonded into a suitable matrix. The matrix
material can be the epoxy or polyester resins or metals, such as
aluminum and magnesium. However, in the high vacuum environment
necessary for efficient operation of the present device, a matrix
material relatively free of out-gassing is required to avoid
degrading the vacuum. Protection of a normally out-gassing matrix
with a thin layer of vacuum deposited metal or other low vapor
pressure material is found to be useful.
Unlike any battery, the performance of the present energy storage
device is virtually unaffected by the number of charge/recharge
cycles, the ambient temperature, or by the rate of charge or
discharge. The efficiency of energy storage is virtually 100
percent, since the only losses are the aerodynamic losses on the
spinning rotor in the vacuum environment and the losses resulting
from bearing drag, which should be minimal at the zero loading of
the magnetic suspension. The overall efficiency of an energy
storage system using the present device is substantially greater
than the efficiency of batteries, presently available flywheel
systems, or any other known energy storage system.
An energy storage system configuration which utilizes the present
energy storage device and which overcomes certain disadvantages of
the system 65 described hereinabove is shown in FIG. 12. The system
shown is seen to utilize an optimized bar 34a spinning in a vacuum
environment maintained by a vacuum can 100 having flared ends
defined by the gimbal limits of the bar 34a. The bar 34a is
gimballed internally in the same fashion previously described for
the bar 34 of FIGS. 5a and 5b. In this system configuration, shaft
members 50a actually pass through openings 108 and 110 in the upper
and lower portions of the can 100, the openings 108 and 110 being
circular and having their centers coincident with the axis of
rotation of the bar 34a. Magnetic fluid seals 112, such as those
described by Rosensweig in U.S. Pat. No. 3,215,572, allow operation
of the bar 34a at the necessary vacuum within the can 100. The
seals 112 provide sealing between the internal vacuum in the can
100 and ambient air with virtually no leakage (less than
10.sup.-.sup.11 cm/sec). The seals 112 not only permit rotation in
a low drag environment, but also allow the placement of bearings
externally of the vacuum can 100, where available high speed
bearings and conventional high speed lubrication may be used.
Since there is no solid contact between the seal 112 and the
rotating shaft, the contribution of the seal to the overall drag is
extremely low and can actually be calculated according to:
P = (.pi./4) .eta. N (.delta.'/.delta.) D.sup.3 .omega..sup.2 l
where:
.eta. = viscosity of seal fluid: poise
N = Number of stages
D = Diameter: cm
.omega. = Rotating speed: rad/sec
.delta. = seal gap
.delta.'= seal width
P = Drag: dyne-cm/sec
Referring again to FIG. 12, high speed bearings 124 are disposed
externally of the vacuum can 100. Since the drive shaft i.e., the
lower shaft member 50a also extends externally of the can 100,
rotor spin-up and power take-off is accomplished in a more direct
fashion than is possible with the system 65 of FIG. 10. Loading on
the bearings 124 is minimized to reduce bearing drag by providing
complete gravity unloading of said bearings through the use of a
passive magnetic suspension 126. The magnetic suspension 126
accommodates only the static load situation, the dynamic loads
being accommodated by the conventional bearings 124.
FIG. 13 illustrates the general concept underlying an
unconventional bearing 128 which can be expected to exhibit reduced
drag loss capability and have a virtually infinite operating life.
The bearing 128 is completely passive and avoids solid contact
between any moving parts. The bearing 128 generally provides
stability in three planes through the use of a permanent annular
ring magnet 130. The magnet 130 provides stability in two planes,
while stability in the third plane is provided by a fluid 132, such
as air sealed by magnetic fluid which is trapped by the magnetic
field of the magnet 130. An arrangement of concentric magnetic
fluid seals shown at 134 similar to the seal 112 previously
described assists in entrapment of the fluid 132.
The bearing 128 may be used in the system of FIG. 12 with the
conventional high speed bearings 124 primarily to obtain lower drag
loss in the static loading condition to minimize rotor run-down
time. The bearing 128 shown is seen to have an annular plate 136
formed integrally with a rotating shaft 138, which shaft 138 also
provides the shaft support for the spinning rotor and serves for
rotor spin-up and power take off. The plate 136, composed of
magnetizable material, has an annular depression 140 formed in one
face thereof and defined by two raised concentric beveled ridges
142. Opposing the ridges 142 and held fixedly at a finite distance
therefrom are concentric annular pole pieces 144 held in spaced
relation by and contiguous to the annular ring magnet 130. The
magnet 130 and pole piece 144 combination is fixedly attached to a
stationary support 148 and surrounds a portion of the rotating
shaft 138. A ferromagnetic fluid 150, which comprises the
concentric fluid seals 134, is held magnetically in the finite
space between the ridges 142 and beveled edges 152 of the pole
pieces 144, thus sealing a chamber 154 defined by the ridges 142
and edges 152. This sealing function is accomplished in the same
fashion as that described for the seal 112 of FIG. 12. The chamber
154 is reduced in volume by the provision of non-magnetic filler
members 156 on either side of the chamber 154. The structure
described thus produces a reduced chamber 154 which holds the
previously mentioned fluid 132. The fluid 132 within the chamber
154 is trapped and held at moderate pressures for indefinite
periods. An operable bearing 128 typically seals a 0.005-inch gap
of air at pressures near 3 psi within the chamber 154. Provision of
a plurality of chambers allows scalable staging of the bearing 128
to a desired loading capability. The bearings 128 are usually
arranged in opposing pairs in order to conveniently maintain axial
stability.
FIG. 14 depicts a multiple rotor energy storage device 200 which
combines a number of advantageous features of the present
invention. The device 200 is seen to comprise a plurality of
optimized cylindrical rotors 202 individually gimballed on an
enlarged portion 203 of a rotary shaft 204 according to the
internal gimbal arrangement previously shown in FIGS. 5a and 5b.
Each rotor 202 is constructed according to the invention, being
composed of a large number of filaments having their respective
longitudinal axes disposed parallel to the longitudinal axis of the
rotor. The rotors 202, as shown, are cylindrical in cross section,
having a greater diameter at and near the center of the rotor and
tapering symmetrically to reduced end portions 206. It should be
understood that the rotors 202 could take shapes other than the
tapering cylindrical form shown, the cylindrical shape being used
mainly for illustrative purposes.
The rotors 202, as better seen in FIGS. 15a and 15b, are
individually gimballed on the shaft 204. Each rotor 202 has an
internal hub 208 comprising a hollow cylinder 210 which receives
the rotor through an axial opening 212 in the cylinder 210. Each
rotor 202 is preferably held within the cylinders 210 by means of
an elastic sleeve 214 disposed over that portion of the rotor's
surface held within the cylinder, i.e., in the fashion previously
described for the embodiment of the invention shown in FIGS. 5a and
5b. Each rotor and hub combination is centered within one of a
number of substantially oval-shaped ports 216 regularly disposed in
the enlarged portion 203 of the shaft 204. The ports 216 are
interdigitated along the length of the portion 203. Thus, if the
rotors 202 were numbered along the shaft 204, those rotors
occupying even-numbered positions would be mutually parallel.
Similarly, those rotors 202 occupying odd-numbered positions would
be mutually parallel. Any odd-numbered rotor would be spatially
perpendicular to any even-numbered rotor.
Each cylinder 210 has two gimbal pins 218 extending from
diametrically opposite points thereon, the pins 218 being aligned
through the mass (and geometrical) center of the rotor and hub
combination. The pins 218 are rotatably received within recesses
220 disposed in the shaft 204, two each of the recesses 220 being
aligned and centered on opposite sides of each of the ports 216.
The longitudinal axis of each pair of aligned recesses 220 is
perpendicular to the longitudinal axis of the ports 216. As is
clearly seen in FIG. 15a, the ports 216 may have portions of their
volume shared with the perpendicular ports 216 on either side
thereof. Although this space sharing arrangement is not necessary,
it does allow the most compact positioning of rotors 202 per unit
length of shaft 204.
FIG. 15b illustrates the degree of freedom allowed by the internal
gimbal arrangement, the magnitude of this motion being dependent on
the design parameters desired for a particular application. Using
the device 200 shown, the shaft 204 need not be externally gimbaled
to avoid precessional loading. Of course, the device 200 could be
constructed without the internal gimballing feature, i.e., each
rotor 202 could be fixed on the shaft 204. In such an event, the
shaft itself would then be externally gimbaled. The structure of
the device 200 also allows provision of a useful safety feature. If
one of the rotors 202 were longer than the remaining rotors, the
longer rotor would fail prior to the attainment of the design
limitations of the device 200 itself. That is, the stresses on the
longer rotor under a certain set of operating conditions are
greater, thus maximizing the probability of a relatively safe
failure of this single rotor rather than the substantially
simultaneous failure of a number of the rotors. The failure of the
longer rotor, or of any individual rotor, signals shutdown of the
device 200 to prevent further failure. In any event, failure of
several of the rotors 202 is an unlikely occurrence, the device 200
being substantially more safe at rotation rates approaching design
limitations than the other embodiments of the invention described
herein.
Uses of the present energy storage device too numerous to mention
are possible. Rotor configurations other than those explicitly
described but which embody the uniaxial, anisotropic filaments
disposed substantially parallel to each other and to the major
stress component acting on the filaments are also possible. Thus,
the invention may be practiced in fashions other than that
specifically outlined herein without departing from the invention
as defined by the following claims.
* * * * *