U.S. patent number RE41,142 [Application Number 10/113,135] was granted by the patent office on 2010-02-23 for composite conformable pressure vessel.
This patent grant is currently assigned to Alliant Techsystems Inc.. Invention is credited to John D. Bennett, Michael D. Blair, Kevin W. Davis, Richard K. Kunz, Darrel G. Turner, Mark J. Warner, F. Edward Wolcott.
United States Patent |
RE41,142 |
Blair , et al. |
February 23, 2010 |
Composite conformable pressure vessel
Abstract
A pressure vessel for holding a pressurized fluid such as
compressed natural gas ("CNG") includes two end cells and zero or
more interior cells. The cell geometry ensures that the cells meet
one another at tangential circular surfaces, thereby reducing the
tendency of adjacent cells to peel apart. A web secured about the
cells includes two sheets that are tangent to the cells. Unused
volumes between the cells and the web contain wedges of foam or
rubber. A valve provides fluid communication between the interior
of the pressure vessel and a pressurized fluid line. The filled
weight of one pressure vessel does not exceed the filled weight of
a conventional gasoline tank that occupies substantially the same
space as the pressure vessel. The pressure vessel may be configured
with exterior recesses for engaging conventional gasoline tank
straps.
Inventors: |
Blair; Michael D. (North Ogden,
UT), Turner; Darrel G. (Perry, UT), Kunz; Richard K.
(North Ogden, UT), Warner; Mark J. (Brigham City, UT),
Davis; Kevin W. (Ogden, UT), Wolcott; F. Edward
(Providence, UT), Bennett; John D. (Brigham City, UT) |
Assignee: |
Alliant Techsystems Inc.
(Minneapolis, MN)
|
Family
ID: |
23509238 |
Appl.
No.: |
10/113,135 |
Filed: |
March 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
08382502 |
Feb 2, 1995 |
05577630 |
Nov 26, 1996 |
|
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Current U.S.
Class: |
220/581; 220/586;
220/564; 220/562; 220/23.2 |
Current CPC
Class: |
B60K
15/03006 (20130101); F17C 1/02 (20130101); F17C
1/16 (20130101); F17C 2221/033 (20130101); F17C
2205/0326 (20130101); F17C 2209/227 (20130101); F17C
2201/035 (20130101); F17C 2203/0619 (20130101); F17C
2260/018 (20130101); B60K 2015/03151 (20130101); F17C
2203/0604 (20130101); F17C 2250/072 (20130101); F17C
2270/0168 (20130101); F17C 2203/0658 (20130101); F17C
2260/011 (20130101); F17C 2201/0166 (20130101); F17C
2203/0646 (20130101); F17C 2205/0142 (20130101); F17C
2203/0636 (20130101); F17C 2201/056 (20130101); F17C
2223/036 (20130101); F17C 2209/221 (20130101); F17C
2223/0123 (20130101); F17C 2201/0171 (20130101); F17C
2260/012 (20130101); F17C 2201/0152 (20130101); F17C
2203/0639 (20130101); F17C 2203/0663 (20130101); F17C
2205/0317 (20130101); F17C 2205/0103 (20130101) |
Current International
Class: |
B65D
8/00 (20060101) |
Field of
Search: |
;220/586,585,584,581,565,564,562,23.4,4.13,23.2,507,503 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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31 51 425 |
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Jun 1983 |
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0 687 587 |
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May 1995 |
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EP |
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1290641 |
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Sep 1962 |
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FR |
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1522609 |
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Aug 1978 |
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GB |
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2032506 |
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May 1980 |
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GB |
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2040430 |
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Aug 1980 |
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GB |
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51-15221 |
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Feb 1976 |
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JP |
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59-27922 |
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Feb 1984 |
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JP |
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05-346198 |
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Dec 1993 |
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JP |
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6 241 397 |
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Aug 1994 |
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JP |
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51771 |
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Nov 1932 |
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NO |
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140943 |
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Sep 1979 |
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NO |
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Other References
English translation of DE 3151425 C1, previously cited. cited by
other .
PCT International Search Report dated Apr. 22, 1996. cited by other
.
Translation of Official Action dated Nov. 24, 1997 from the
Norwegian Patent Office. cited by other .
Supplementary European Search Report dated Sep. 10, 1998. cited by
other .
Norwegian Search Report of Jan. 13, 2004, and English translation
of the Official Action of the Norwegian Patent Office dated Jan.
19, 2004. cited by other.
|
Primary Examiner: Castellano; Stephen J.
Attorney, Agent or Firm: TraskBritt
Claims
What is claimed and desired to be secured by patent is:
1. A pressure vessel comprising: .Iadd.a plurality of cells
including .Iaddend.at least two end cells, .Iadd.each cell being in
contact with at least one adjacent cell, .Iaddend.each end cell
having a cross-section comprising: an arcuate outer wall defining a
substantially constant outer wall radius; and an arcuate upper wall
having an end unitary with said outer wall at an upper-outer
junction, said upper wall defining a substantially constant upper
wall radius which is less than said outer wall radius; .[.and.]. a
web secured about said end cells, said web comprising a
substantially planar upper sheet which is generally tangent to said
upper-outer junction of each of said end cells.Iadd.; and at least
one discrete wedge substantially conformally filling a void
substantially defined by said upper sheet of said web and portions
of two adjacent cells.Iaddend..
2. The pressure vessel of claim 1, wherein said end cells comprise
a composite material.
3. The pressure vessel of claim 1, wherein said web comprises a
composite material.
4. The pressure vessel of claim 1, wherein each of said end cells
comprises a substantially semi-cylindrical portion.
5. The pressure vessel of claim 1, wherein said outer wall radius
is substantially the same for each of said outer walls and said
upper wall radius is substantially the same for each of said upper
walls.
6. The pressure vessel of claim 1, wherein an interior cell is
secured adjacent at least one of said upper walls of said end
cells, and said web is secured about said interior cell.
7. The pressure vessel of claim 6, wherein a portion of said
interior cell adjacent said web has a substantially semicircular
upper cross-section.
8. The pressure vessel of claim 7, wherein said substantially
semi-circular upper cross-section of said interior cell is
generally tangent to at least one of said upper walls of said end
cells.
9. The pressure vessel of claim 7, wherein a radius of said
substantially semi-circular upper cross-section of said interior
cell is substantially equal to said upper wall radius of at least
one of said upper walls.
10. The pressure vessel of claim 1, wherein at least two interior
cells are secured between said end cells, each of said upper walls
of said end cells is adjacent at least one of said interior cells,
and said web is secured about said interior cells.
11. The pressure vessel of claim 1, .[.further comprising a.].
.Iadd.wherein said at least one discrete .Iaddend.wedge .[.disposed
between said upper sheet of said web and at least one of said upper
walls for resisting forces that urge said upper sheet toward said
upper wall.]. .Iadd.comprises at least one member selected from the
group consisting of a rubber and a resilient foam.Iaddend..
12. A pressure vessel comprising: .Iadd.a plurality of cells
including .Iaddend.at least two composite end cells, .Iadd.each
cell being in contact with at least one adjacent cell,
.Iaddend.each end cell having a cross-section comprising: an
arcuate outer wall defining a substantially constant outer wall
radius; an arcuate upper wall having an end unitary with said outer
wall at an upper-outer junction, said upper wall defining a
substantially constant upper wall radius which is less than said
outer wall radius; an arcuate lower wall having an end unitary with
said outer wall at a lower-outer junction, said lower wall defining
a substantially constant lower wall radius which is less than said
outer wall radius; and an inner wall having an upper end unitary
with said upper wall and having a lower end unitary with said lower
wall; .[.and.]. a composite web .[.secured about.]. .Iadd.securing
.Iaddend.said end cells, said web comprising a substantially planar
upper sheet which is generally tangent to said upper-outer junction
of each of said end cells, and a substantially planar lower sheet
which is generally tangent to said lower-outer junction of each of
said end cells.Iadd., and wherein a portion of said web transitions
into, and is conjoined with, a portion of said arcuate outer wall
of at least one of said at least two composite cells to define a
unitary structure; and a discrete wedge substantially conformally
filling a void substantially defined by said upper sheet of said
composite web and portions of two adjacent cells.Iaddend..
13. The pressure vessel of claim 12, wherein said upper wall radius
and said lower wall radius are substantially equal.
14. The pressure vessel of claim 12, wherein an interior cell is
secured adjacent at least one of said upper walls and adjacent at
least one of said lower walls, and said web is secured about said
interior cell.
15. The pressure vessel of claim 14, wherein a portion of said
interior cell adjacent said web has a substantially semi-circular
upper cross-section which is generally tangent to said upper wall
of at least one of said end cells and a substantially semi-circular
lower cross-section which is generally tangent to said lower wall
of the same one of said end cells.
16. The pressure vessel of claim 12, further comprising a valve
capable of selectively providing fluid communication between an
interior chamber of said pressure vessel and an exterior
pressurized fluid line connected to said valve.
17. A pressure vessel comprising: .Iadd.a plurality of cells
including .Iaddend.at least two composite end cells, .Iadd.each
cell being in contact with at least one adjacent cell,
.Iaddend.each of said end cells comprising a substantially
semi-cylindrical portion, each of said end cells having a
cross-section comprising: a substantially semi-circular outer wall
having an outer wall radius; a substantially quarter-circular upper
wall having an upper wall radius less than said outer wall radius,
said upper wall having an end unitary with said outer wall at an
upper-outer junction; a substantially quarter-circular lower wall
having a lower wall radius substantially equal to said upper wall
radius, said lower wall having an end unitary with said outer wall
at a lower-outer junction; and a substantially straight inner wall
having an upper end unitary with said upper wall and having a lower
end unitary with said lower wall; .[.and.]. a composite web
.[.secured about.]. .Iadd.securing .Iaddend.said end cells, said
web comprising a substantially planar upper sheet which is
generally tangent to said upper-outer junction of each of said end
cells, and a substantially planar lower sheet which is generally
tangent to said lower-outer junction of each of said end
cells.Iadd., and wherein a portion of said web transitions into,
and is conjoined with, a portion of said arcuate outer wall of at
least one of said at least two composite cells to define a unitary
structure; and a discrete upper wedge substantially conformally
filling a void substantially defined by said upper sheet of said
composite web and portions of two adjacent cells.Iaddend..
18. The pressure vessel of claim 17, further comprising .[.an upper
wedge disposed between said upper sheet of said web and at least
one of said upper walls for resisting forces that urge said upper
sheet toward said upper wall, and.]. a .Iadd.discrete
.Iaddend.lower wedge disposed between said lower sheet of said web
and at least one of said lower walls for resisting forces that urge
said lower sheet toward said lower wall.
19. The pressure vessel of claim 17, wherein at least two interior
cells are secured between said end cells, each of said upper walls
of said end cells is adjacent at least one of said interior cells,
and said web is secured about said interior cells.
20. The pressure vessel of claim 19, wherein a portion of each of
said interior cells has a substantially semi-circular upper
cross-section adjacent said upper sheet of said web, at least one
of said substantially semi-circular upper cross-sections is
generally tangent to at least one of said upper walls of said end
cells, each of said interior cells has a substantially
semi-circular lower cross-section adjacent said lower sheet of said
web, and at least one of said substantially semi-circular lower
cross-sections is generally tangent to at least one of said lower
walls of said end cells.
21. The pressure vessel of claim 17, wherein the filled weight of
said pressure vessel does not exceed the filled weight of a
gasoline tank that occupies substantially the same volume envelope
as said pressure vessel.
22. The pressure vessel of claim 17, wherein said pressure vessel
is configured with fixtures defining exterior recesses capable of
engaging gasoline tank straps which are capable of securing said
pressure vessel to the vehicle.
23. The pressure vessel of claim 17, wherein said cells of said
pressure vessel are configured with at least one port which
provides fluid communication between the interiors of said
cells.
24. The pressure vessel of claim 17, wherein said cells of said
pressure vessel are configured with an external manifold which
provides fluid communication between the interiors of said
cells.
25. The pressure vessel of claim 17, further comprising a valve
capable of selectively providing fluid communication with an
interior chamber of said pressure vessel.
26. The pressure vessel of claim 25, wherein said valve comprises a
fusible plug.
27. The pressure vessel of claim 25, wherein said valve comprises a
mechanical pressure relief mechanism which is configured to bleed
off pressurized fluid at a set predetermined pressure.
.Iadd.28. The pressure vessel of claim 12, wherein said discrete
wedge comprises at least one member selected from the group
consisting of a rubber and a resilient foam..Iaddend.
.Iadd.29. The pressure vessel of claim 12, wherein each of said end
cells comprises an end with a respective individual end
cap..Iaddend.
.Iadd.30. The pressure vessel of claim 12, wherein said pressure
vessel optionally comprises at least one interior cell comprising
an inner wall, and wherein said inner walls of said end cells and
said optional interior cell are each configured with at least one
port for providing fluid communication between said
cells..Iaddend.
.Iadd.31. The pressure vessel of claim 12, wherein said end cells
of said pressure vessel are configured with an external manifold
which provides fluid communication between said cells..Iaddend.
.Iadd.32. The pressure vessel of claim 12, wherein the composite
cell wall comprises preimpregnated tow wound around said liner with
a combination of hoop and helical windings..Iaddend.
.Iadd.33. The pressure vessel of claim 18, wherein said discrete
upper wedge and said discrete lower wedge each comprises at least
one member selected from the group consisting of a rubber and a
resilient foam..Iaddend.
.Iadd.34. The pressure vessel of claim 17, wherein each of said end
cells comprises an end with a respective individual end
cap..Iaddend.
.Iadd.35. The pressure vessel of claim 17, wherein the composite
cell wall is formed from preimpregnated tow wound around said liner
with a combination of hoop and helical windings..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to a pressure vessel for holding
compressed fluids, and more particularly to a composite pressure
vessel having a plurality of storage cells which meet tangentially
within a composite web to closely and efficiently approximate a
rectangular volume.
TECHNICAL BACKGROUND OF THE INVENTION
Pressure vessels are widely used to store liquids and gases under
pressure. The storage capacity of a pressure vessel depends on the
internal volume of the pressure vessel and the pressure the vessel
is capable of safely containing. In addition to its storage
capacity, the size, internal shape, external shape, and weight of
the pressure vessel are often important in a particular
application.
One growing application of pressure vessels is the storage of
compressed natural gas ("CNG"). CNG is increasingly viewed as
preferable to gasoline for fueling vehicles. CNG generally burns
cleaner than gasoline, leading to a visible reduction in air
pollution and corresponding reductions in health care costs.
Natural gas is also a relatively abundant fuel. Accordingly,
approaches have been devised for converting gasoline-fueled
vehicles by retrofitting them to use CNG instead of gasoline.
Known approaches to retrofitting a vehicle for use with CNG include
replacing the gasoline tank with conventional natural gas storage
cylinders. Unfortunately, the use of conventional CNG cylinders
restricts the driving range of the converted vehicle to about 120
to 140 miles, which severely limits consumer acceptance of such
conversions. The driving range of such a converted vehicle could be
increased by simply adding more CNG storage cylinders. This could
be done, for example, by mounting the additional CNG cylinders
within the trunk of the vehicle. However, it is generally desirable
to fit the CNG storage cylinders within the limited space
previously occupied by the gasoline tank.
One suggested approach for increasing the vehicle's driving range
is to carry more CNG within the same storage cylinders. This is
accomplished by pumping more CNG into the storage cylinders,
thereby increasing the pressure within the storage cylinders.
However, increasing the storage pressure often requires thickening
the walls of the storage cylinders to provide them with sufficient
structural strength to resist the higher pressure. Increasing the
wall thickness requires either an increase in the external size of
the storage cylinders, thereby preventing storage of the cylinders
in the space previously occupied by the gasoline tank, or a
reduction of the internal storage volume of the cylinders, thereby
reducing the volume of stored CNG and hence reducing the vehicle's
driving range. Thickening the walls also increases the weight of
the storage cylinders, thereby decreasing the fuel efficiency of
the vehicle.
Other approaches to increasing the driving range of vehicles fueled
by CNG propose varying the shape of CNG storage containers.
Currently, spheres, cylinders, and certain combinations of
spherical and cylindrical sections are favored. As illustrated in
FIGS. 1 and 2, one conventional pressure vessel 100 includes
several lobes 102 secured together. Each lobe 102 is geometrically
defined as a portion of a "tube-and-dome" shape. Geometrically, a
tube-and-dome includes a straight tube 104 which is circular with
radius R in transverse cross-section (see FIG. 2). Two lobes 102
are combined by slicing each lobe 102 along a plane 106 that is
parallel to the longitudinal axis 108 of the tube 104. The
truncated faces of the two lobes 102 are then secured against one
another. Each of one or more center lobes 110 is thus sliced along
two planes 106 parallel to the longitudinal axis 112 of the center
lobe's tube. In the resulting container 100, the lobes 102 are not
tangent to one another at junctions 114 where they meet. Each tube
104 is capped at each end by a portion of a hemispherical dome 116
having the same radius R as the tube 104.
Such tube-and-dome containers have several drawbacks when employed
in applications requiring substantially rectangular angular
pressure vessels. Such applications include, but are not limited
to, storage of CNG for use in fueling a vehicle. The vehicle may be
a vehicle retrofitted with CNG tanks after previously being fueled
by gasoline, or it may be a vehicle designed from the start to run
on CNG.
The drawbacks of tube-and-dome geometry arise from differences
between that geometry and a substantially rectangular geometry. In
the case of retrofitted vehicles, the desire for substantially
rectangular vessels arises because many gasoline tanks are shaped
like substantially rectangular shells, as illustrated generally by
a phantom rectangular shell 118 in FIGS. 1 and 2. In the case of
vehicles designed initially to use CNG, the preference for a
substantially rectangular pressure vessel may arise from other
design considerations. In either case, a single tube-and-dome lobe
102 is a very poor approximation to such rectangular volumes.
Arranging truncated portions of several tube-and-dome lobes 102
together to form the pressure vessel 100 improves the
approximation, but large wedge-shaped unused volumes 120
nonetheless remain which are not used for CNG storage. The unused
volumes 120, which are defined by the circular walls of adjacent
tube-and-dome lobes 102, may occupy a significant percentage of the
internal volume of the rectangular shell 118. Eliminating the
unused volumes 120 entirely would require a CNG container which is
substantially a rectangular shell in shape. But building a
rectangular shell-shaped CNG vessel sufficiently strong to resist
typical CNG storage pressures would require excessively thick
walls, because the rectangular shell is so far removed in shape
from a sphere.
In addition to the unused volumes 120, the vessel 100 has the
disadvantage that the lobes 102 tend to peel apart at the junctions
114 because of stresses that occur at the junctions 114. Thickening
the walls of the lobes 102 to overcome the peeling tendency reduces
the storage capacity of the container 100 or increases its size,
and also increases the container's weight.
Thus, it would be an advancement in the art to provide a pressure
vessel which approximates a rectangular volume.
It would also be an advancement to provide such a pressure vessel
which facilitates the retrofitting of gasoline vehicles by having
an external shape compatible with the rectangular shell shape of
the exterior of the gasoline tank.
It would be a further advancement to provide such a pressure vessel
which has generally circular cross-sections.
It would also be an advancement to provide such a pressure vessel
that resists the tendency to peel apart when subjected to internal
storage pressures.
Such a pressure vessel is disclosed and claimed herein.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a pressure vessel having a novel
geometry. In one embodiment, the pressure vessel is configured to
resist pressure from compressed natural gas ("CNG") stored within
the vessel and the vessel approximates the rectangular shape of a
conventional gasoline tank. The pressure vessel resists a normal
operating pressure of up to about 3,600 p.s.i. and has sufficient
burst strength to resist about three times the normal operating
pressure, namely, a burst strength of about 11,000 p.s.i.
The novel geometry of the present pressure vessel is described
herein through reference to geometric operations such as slicing a
shape with a plane. These geometric operations do not necessarily
correspond to manufacturing methods, but are rather illustrations
of the geometry of the pressure vessel to be manufactured.
One embodiment of the pressure vessel includes two end cells. Each
end cell includes a semi-cylindrical outer wall. The outer wall
geometry is defined by slicing a first cylindrical container with a
plane through its longitudinal axis to create a half-cylinder. Each
end cell also includes a quarter-cylindrical upper wall and a
quarter-cylindrical lower wall. The upper wall and lower wall are
unitary with the outer wall. The upper wall geometry is defined by
slicing a second cylindrical container which has the same length as
the first cylindrical container but which also has a smaller
radius. The second cylindrical container is sliced with two
perpendicular planes through its longitudinal axis. The lower wall
is similarly defined by slicing a third cylindrical container with
two perpendicular planes. A rectangular section connects the lower
end of the upper wall with the upper end of the lower wall. The end
of each cell thus defines a curve which is herein denoted a
"polyradial" curve, in reference to the differing radii of the
outer and upper-or-lower walls.
Each end of the joined half- and quarter-cylindrical walls is
capped by a cap. Each cap corresponds in shape (not necessarily in
materials actually employed) to an elastic sheet secured to a
closed polyradial curve as a boundary condition and then subjected
to a uniform deformation pressure.
The novel geometry of the present invention is further illustrated
by a cross-section taken transverse to the longitudinal axis of one
of the end cells. The cross-section defines a polyradial curve
which includes an arcuate outer wall, an arcuate upper wall, and an
arcuate lower wall. The outer wall corresponds to the semi-cylinder
with the larger radius, which is therefore termed the outer wall
radius. The upper wall, which has one end unitary with the outer
wall at an upper-outer junction, corresponds to the upper
quarter-cylinder, and thus has an upper wall radius that is less
than the outer wall radius. The lower wall, which has one end
unitary with the outer wall at a lower-outer junction, corresponds
to the lower quarter-cylinder. In this embodiment the lower wall
radius is equal to the upper wall radius, but these radii may
differ in other embodiments. Thus, in general a polyradial
cross-section may include circular arcs having either two or three
different radii.
Alternative embodiments of the pressure vessel include one or more
interior cells secured between the end cells. In cross-section,
each interior cell has a semi-cylindrical upper portion secured to
a semi-cylindrical lower portion by two straight inner walls. The
interior cells are secured tangent to and adjacent to one another,
with the end cells secured tangent to and adjacent to the outermost
interior cells.
The radii of the semi-cylindrical interior wall upper and lower
portions are the same as the radii of the quartercylindrical upper
wall and lower wall, respectively, of the end cells. Thus, the end
cells and interior cells of the present pressure vessel are
generally tangent to one another where they meet, unlike the lobes
of previously known pressure vessels. This aspect of the novel
geometry of the present pressure vessel reduces the tendency of
adjacent cells to peel apart.
A web is secured about the end cells and about any interior cells
that are present. The web includes a substantially planar upper
sheet which is generally tangent to the upper-outer junction of
each of the end cells and to the semi-cylindrical upper portion of
each interior cell. The web also includes a substantially planar
lower sheet which is generally tangent to the lower-outer junction
of each of the end cells and to the semi-cylindrical lower portion
of each interior cell. The web strengthens the pressure vessel by
assisting in holding the cells tangent to one another and by
reinforcing the cell walls.
The pressure vessel of the present invention defines wedge-shaped
unused volumes between the web and the cells that are not used for
pressurized fluid storage. In one embodiment, the pressure vessel
is strengthened by substantially filling the unused volumes with
wedges of foam or rubber disposed between the web sheets and the
cells.
The pressure vessel of the present invention includes a valve
capable of selectively providing fluid communication between an
interior chamber of the pressure vessel and an exterior pressurized
fluid line such as a CNG line connected to the valve. The interiors
of the several cells that form the present pressure vessel are
configured to be in fluid communication with one another, so that
only one valve is needed to control fluid flow in and out of the
pressure vessel. The valve includes a pressure relief mechanism to
bleed off pressurized fluid if the internal pressure of the
pressure vessel exceeds a predetermined value. The valve also
includes a fusible plug to provide emergency venting in the
presence of high temperatures.
Advantageously, the pressure vessel of the present invention
facilitates retrofitting gasoline-fueled vehicles because the
filled weight of the pressure vessel does not exceed the filled
weight of a conventional gasoline tank occupying substantially the
same volume envelope. In addition, the pressure vessel may be
configured with fixtures defining exterior recesses capable of
engaging conventional gasoline tank straps. Thus, the same tank
straps previously used to secure the gasoline tank to the vehicle
can be used, without substantial alteration or further testing, to
secure the pressure vessel to the vehicle.
Those of skill in the art will appreciate that the pressure vessel
of the present invention is not limited to use in retrofitting
vehicles. The present invention also has applications in the design
of new vehicles, as well as in other applications which benefit
from the use of pressure vessels having a substantially rectangular
shape.
Pressure vessels according to the present invention are
manufactured with metal or composite parts. In one embodiment, the
cells are formed of a liner such as a metallic foil or a synthetic
polymer film to provide gas impermeability. The liner is
overwrapped by a composite layer using filament winding or another
method familiar to those of skill in the art. Interior ports may be
provided in the cell walls for fluid communication between cells,
or an external manifold may be subsequently attached to provide
such communication. The cells are positioned adjacent one another,
and all the cells are then overwrapped by a composite web. The
composite used in the cells, the web, or both may include carbon,
glass, graphite, aramid, or other known fibers bound in a
thermoplastic or thermoset resin.
In another embodiment, the cells are formed of metal by stamping,
extruding, or another process familiar to those of skill in the
art. The metal pieces are welded together, and are then overwrapped
with a composite web. Examples of suitable metals are titanium,
aluminum, and steel.
In summary, the present invention provides a pressure vessel in
which the cells meet tangentially and are over-wrapped with a
reinforcing web. The novel geometry of the pressure vessel provides
generally circular cross-sections which resist the tendency to peel
apart in response to internal pressure. The exterior of the
pressure vessel conforms generally to the external shape of a
conventional gasoline tank and includes fixtures defining recesses
to engage conventional gasoline tank straps.
The features and advantages of the present invention will become
more fully apparent through the following description and appended
claims taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
To illustrate the manner in which the advantages and features of
the invention are obtained, a more particular description of the
invention summarized above will be rendered by reference to the
appended drawings. Understanding that these drawings only provide
selected embodiments of the invention and are not therefore to be
considered limiting of its scope, the invention will be described
and explained with additional specificity and detail through the
use of the accompanying drawings in which:
FIG. 1 is a perspective view of a prior art pressure vessel;
FIG. 2 is a cross-section taken along line 2--2 in FIG. 1;
FIG. 3 is a partial cut-away perspective view of one embodiment of
the pressure vessel of the present invention;
FIG. 4 is a transverse cross-section of a portion of the pressure
vessel taken along line 4--4 in FIG. 3;
FIG. 5 is a sectioned perspective view of a first alternative
embodiment of a pressure vessel of the present invention;
FIG. 6 is a sectioned perspective view of a second alternative
embodiment of a pressure vessel of the present invention;
FIG. 7 is an exploded perspective view illustrating selected
components of the embodiment shown in FIG. 3; and
FIG. 8 is a partial cut-away perspective view of an alternative
embodiment of a pressure vessel of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is now made to the figures wherein like parts are
referred to by like numerals. The present invention relates to a
pressure vessel generally, and more specifically to a tank for
holding compressed natural gas ("CNG") for fueling a vehicle (not
shown). One embodiment of the present pressure vessel is indicated
generally at 10 in FIG. 3. This embodiment of the pressure vessel
10 includes three cells 12 secured within a web 14. The three cells
12 include a left end cell 16, a right end cell 18, and one
interior cell 20. The cells 12 have a novel geometry and other
important characteristics which will be described in detail after
the other main components of the pressure vessel 10 are noted.
The right end cell 18 is preferably configured with a valve 22 to
control fluid flow in and out of the pressure vessel 10. The valve
22 preferably includes pressure relief means for the controlled
release of pressurized fluid from the pressure vessel 10 if the
internal pressure of the pressure vessel 10 exceeds a predetermined
value. In one embodiment the pressurized fluid is CNG and the
predetermined value for controlled fluid release is about 3,600
p.s.i.
Suitable pressure relief means include a mechanical pressure relief
mechanism of the type familiar in the art which is configured to
bleed off CNG at a set predetermined pressure. Suitable pressure
relief means also preferably includes a fusible plug to provide
emergency venting in the presence of high temperatures, such as
temperatures which could raise the pressure within the pressure
vessel 10 above the predetermined value. It is presently preferred
that the fusible plug be configured to provide emergency venting
when temperatures in the tank rise above about 212 degrees
Fahrenheit. Those of skill in the art will appreciate that the
pressure vessel 10 could also be usefully configured with the valve
22 at another location or with more than one valve.
Wedge-shaped supports 24 are positioned to extend lengthwise
between the cells 12 and the web 14. For clarity of illustration,
portions of these supports 24 have been cut away in FIG. 3. The
supports 24 generally fill the wedge-shaped unused volume between
the cells 12 and the web 14 to provide structural support to the
web 14. Suitable materials for the supports 24 include rubber,
resilient foam, and other rigid or semi-rigid materials familiar to
those in the art.
The exterior of the pressure vessel 10 is configured with fixtures
defining recesses 25 for accepting and retaining conventional
gasoline tank straps (not shown). It is presently preferred in
retrofitting applications that the exterior of the pressure vessel
10 also conform generally in shape to a conventional gasoline tank,
both in its generally rectangular shape and in its dimensions. The
recesses 25 and other conforming features of the pressure vessel 10
facilitate replacement of a conventional gasoline tank with the
pressure vessel 10 during conversion of the vehicle from a
gasoline-fueled configuration to a CNG-fueled configuration.
With reference to FIG. 4, the end cell 18 includes an outer wall 26
disposed about a liner 28. The outer wall 26 is preferably made of
a composite material, such as carbon, glass, graphite, aramid, or
other known fibers bound in a thermoplastic or thermoset resin such
as epoxy. The liner 28 may be made of a gas impermeable material,
such as a metallic foil or a synthetic polymer film.
Although the novel geometry and other characteristics of the
present invention will be described with reference to the end cell
18, other cells 12 of the pressure vessel 10 also include novel
features. The outer wall 26 is generally semi-cylindrical. The
geometry of the outer wall 26 is defined by slicing a first
cylinder with a plane through a longitudinal axis 30. The
longitudinal axis 30 extends through a point 32 perpendicular to
the plane of FIG. 4. The radius 34 of the outer wall 26 is thus
substantially constant through an arc of about 180 degrees.
A generally quarter-cylindrical upper wall 36 and a generally
quarter-cylindrical lower wall 38 are attached to the outer wall
26. The upper wall 36 is unitary with the outer wall 26 at an
upper-outer junction 40, and the lower wall 38 is unitary with the
outer wall 26 at a lower-outer junction 42. The quarter-cylindrical
geometry of the walls 36 and 38 is defined by slicing a second and
third cylinder which each have the same length as the outer wall 26
cylinder but which also have smaller tube radii 44 and 46,
respectively. Each of the second and third cylinders is sliced with
two perpendicular planes through its longitudinal axis to define
the quarter-cylinder.
The upper half of the outer wall 26 and the upper wall 36 thus
define a polyradial curve. The lower half of the outer wall 26 and
the lower wall 38 define a second polyradial curve. In this
presently preferred embodiment, the radius 44 of the upper wall 36
equals the radius 46 of the lower wall 38, but in alternative
embodiments these radii differ. However, the radius 34 of the outer
wall 26 is always larger than either of the radii 44 and 46.
A substantially straight inner wall 48 connects the upper wall 36
and the lower wall 38. The inner wall 48 is unitary with the upper
wall 36 and the lower wall 38 at an upper-inner junction 50 and a
lower-inner junction 52, respectively. The inner wall 48 is
generally tangent to the upper wall 36 at the upper-inner junction
50 and is generally tangent to the lower wall 38 at the lower-inner
junction 52.
The web 14 (FIG. 3) includes an upper sheet 54 which is generally
tangent to the upper wall 36 at the upper-outer junction 40. The
web 14 also includes a lower sheet 56 which is generally tangent to
the lower wall 38 at the lower-outer junction 42. The upper sheet
54 and the upper wall 36 substantially define an unused volume 58
which is not used for storing pressurized fluid. The lower sheet 56
and the lower wall 38 substantially define a similar unused volume
60. The unused volumes 58, 60 are preferably substantially filled
by the wedge-shaped supports 24 (FIG. 3).
As illustrated in FIG. 3, it is presently preferred to configure
each end of each cell 12 with a cap 62. In one embodiment, the caps
62 on the end cells 16, 18 have a geometry which interpolates
smoothly between a portion of a sphere having a radius equal to the
outer wall radius 34, on the one hand, and portions of spheres
having the upper wall radius 44 and the lower wall radius 46, on
the other hand. The geometry of the caps 62 on the interior cell 20
interpolates smoothly between a portion of a sphere having a radius
equal to the outer wall radius 34, on the one hand, and portions of
spheres having the upper wall radius 44 and the lower wall radius
46, on the other hand. In alternative embodiments, the caps 62 have
different geometries which smoothly blend spheres having the three
radii 34, 44, and 46.
In one embodiment, each cap 62 corresponds in shape to a
hypothetical elastic sheet which is secured to the closed
polyradial curve defined by the end of the cell 12 and then
subjected to a uniform deformation pressure. In analytic terms, the
end of the cell 12 defines a boundary condition and the shape of
the cap 62 is determined by manipulating differential equations
corresponding to deformation of the uniform sheet by spatially
uniform forces such as gas pressure. Those of skill will appreciate
that different sheet elasticities may lead to differently-sized
caps, and they will readily choose between these possible shapes
according to the rectangular volume being approximated and other
design constraints.
FIGS. 5 and 6 illustrate two alternative embodiments of the
pressure vessel of the present invention. Each embodiment is shown
sectioned along a line corresponding generally in position to the
line 4--4 in FIG. 3. Although the embodiment shown in FIG. 5
includes a left end cell 16 and a right end cell 18, it includes no
interior cell 20. By contrast, the embodiment shown in FIG. 6
includes a left end cell 16, a right end cell 18, and two interior
cells 20. More generally, embodiments of the pressure vessel of the
present invention may include zero or more interior cells.
As shown in FIG. 6, each interior cell 20 has a substantially
semi-circular upper cross-section 21 which is generally tangent to
either the upper wall 36 of an end cell 16, 18 or to the
semi-circular upper cross-section 21 of another interior cell 20.
Each interior cell 20 also has a substantially semi-circular lower
cross-section 23 which is generally tangent to either the lower
wall 38 of an end cell 16, 18 or to the semicircular lower
cross-section 23 of another interior cell 20. In this embodiment,
the radius of each semi-circular upper cross-section 21
substantially equals the upper wall radius of the upper walls
36.
As illustrated in FIGS. 5-7, the interior chambers of the cells 12
of the pressure vessels may be placed in fluid communication with
one another by one or more ports 64. Thus, the pressure within the
interiors of the cells 12 is equalized, and only one valve 22 is
needed to control the flow or pressurized fluid in and out of the
pressure vessel. An alternative embodiment, illustrated in FIG. 8,
provides fluid communication between the cells 12 through an
external manifold 66. The manifold is constructed of metal or other
familiar materials. In this embodiment, the pressure relief valve
22 and fusible plug are integrated into the manifold 66.
Although the pressure vessels illustrated in FIGS. 3 through 6 are
generally in the form of one row of cylinders, alternative
embodiments employ the novel geometry of the present invention in
pressure vessels having other general forms. For instance, some
embodiments include generally toroidal cells which have in
cross-section the novel geometry of the present invention.
Other embodiments include four end cells rather than two end cells.
In such embodiments, a cross-section of each of the four end cells
includes at least one polyradial curve, and may include two
polyradial curves in the form of a quarter-circular outer wall that
is unitary with two smaller quarter-circular walls. The web is
generally tangent to the end cell at the junctions between the
outer wall and the unitary smaller walls, and the various cells are
generally tangent where they meet one another. Those of skill in
the art may also identify other embodiments according to the
teachings herein.
With reference to FIG. 7, the present pressure vessel is
manufactured by methods familiar to those of skill in the art. One
approach forms the cells 12 by placing the liner 28 (FIG. 4) around
a mandrel (not shown) which has the desired geometry and
dimensions. The desired mandrel geometry, which provides for
tangential meetings between the cells 12 (see FIGS. 5 and 6) and
the other novel geometric features of the present invention, is
readily determined by those of skill in the art according to the
teachings herein.
The desired mandrel dimensions are readily determined by those of
skill in the art from information which includes the strength of
the materials used to form the cells 12, the pressures the cells 12
must resist, and the dimensions of the space into which the
finished pressure vessel must fit. In one embodiment, the materials
used to form the cells 12 include preimpregnated graphite tow which
is wound with a combination of hoop and helical windings to provide
sufficient strength to resist a standard operating pressure within
the pressure vessel of about 3,600 p.s.i. and a burst strength of
about two to three times that pressure. The overall dimensions of
this embodiment of the pressure vessel are generally those of the
conventional gasoline tank (not shown) which the pressure vessel
replaces. The present pressure vessel may also be utilized in
applications other than retrofitting gasoline-fueled vehicles for
CNG usage, in which case criteria other than the size of a
conventional gasoline tank will define the desired dimensions of
the pressure vessel.
After the liner 28 is placed about the mandrel, the liner 28 is
overwrapped by composite material using filament winding, tube
rolling, tape wrapping, automated fiber placement, or another
method familiar to those of skill in the art. Aligned ports 64 may
be configured in the walls of the cells 12 either by machining
after the composite of the cell wall has cured or by placing the
composite fibers around a suitable fixture. The valve 22 is secured
to one of the end cells 18 by a metal polar boss.
The cells 12 are then positioned adjacent one another as shown in
FIG. 3. The rubber or foam supports 24 are placed or glued against
the cells 12. Then the cells 12 are over-wrapped by the composite
web 14. The web 14 includes known composite materials and is
applied by filament winding or another application technique
familiar to those of skill in the art.
The full assembly is then placed in a clamshell mold (not shown).
The mold is generally box-shaped with silicone rubber inserts that
match the inside of the box on one side and the desired exterior
pressure vessel shape on the other. A combination of silicone
insert expansion and pressurization of the cell liners 28 is then
employed to compact the composite material to the desired shape.
Those of skill in the art will appreciate that other manufacturing
techniques may also be employed to form pressure vessels according
to the teachings herein.
In another embodiment, the cells 12 are formed of metal by
stamping, extruding, or another process familiar to those of skill
in the art. The metal pieces are welded together and are then
overwrapped with the composite web 14. Suitable metals include
titanium, aluminum, and steel.
In summary, the present invention provides a pressure vessel which
approximates the internal volume of a conventional gasoline tank.
The geometry of the cells utilizes upper walls and lower walls
whose radii are smaller than the radius of the outer wall. Because
the cells meet tangentially, and because the web is tangential to
the cells and supports the cells, the pressure vessel of the
present invention has generally circular cross-sections that resist
the tendency to peel apart. Moreover, the present pressure vessel
conforms to the external shape of a conventional gasoline tank. The
exterior of the present pressure vessel is generally rectangular
and is provided with fixtures defining recesses to engage the
straps that previously held the gasoline tank to the vehicle.
The invention may be embodied in other specific forms without
departing from its spirit or essential characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not restrictive. Any explanations provided herein
of the scientific principles employed in the present invention are
illustrative only. The scope of the invention is, therefore,
indicated by the appended claims rather than by the foregoing
description. All changes which come within the meaning and range of
equivalency of the claims are to be embraced within their
scope.
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