Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURE VESSEL, HYDROGEN STORAGE TANK AND
METHOD FOR MANUFACTURING PRESSURE VESSEL
TECHNICAL FIELD
The present invention relates to a pressure vessel, a hydrogen storage
tank having an airtight liner and a shell made of fiber reinforced plastic
which is
formed by winding a resin-impregnated fiber bundle outside of the liner for
curing
and having a shape consisting of a cylindrical portion with domed end portions
on
each end, each domed end portion having a boss at its center, and a method for
manufacturing the pressure vessel.
Pressure vessels for containing compressed natural gas (CNG), liquefied
natural gas (LNG), or the like, are generally made of steel, aluminum alloy,
or the
like, and, therefore, they are heavy. Recently, people have gained a growing
awareness of the prevention of global warming. This creates rising demands
particularly on developing hydrogen-fueled cars such as fuel cell electric
vehicles
and hydrogen-fueled engine automobiles for reducing carbon dioxide exhausted
from vehicles.
A hydrogen-fueled automobile generally has a hydrogen storage tank,
which is filled with hydrogen gas, as a hydrogen supply. In this case, a heavy
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pressure vessel for the fuel tank of the hydrogen storage tank lowers fuel
consumption. To eliminate the above inconvenience, a steel gas cylinder having
an airtight finer which is covered with a pressure-resistance shell made of
fiber
reinforced plastic (FRP) has been proposed.
The FRP shell is formed so that a resin-impregnated fiber bundle layer,
which is wound outside of the liner by a filament winding method (hereinafter,
it is
occasionally called "FW method".), is cured. A thin-walled pressure vessel
which
is formed in rotation symmetry has a principal stress in the axial direction
and
to circumferential direction. Thus, for fiber reinforced composite material,
if is
advantageous to arrange the fibers in the direction of principal stress.
Therefore,
fibers F are arranged in such a manner that in-plane winding (shown in FIG. 9)
or
helical winding (not shown) occurs at the domed end portions 51 of the
conventional pressure vessel 50, and the combination of in-plane winding or
helical winding and hoop winding occurs at the cylindrical portion 52.
However, in the case of in-plane winding or helical winding, because all
fibers contact the boss 53 on each end of the pressure vessel 50 and then turn
back, the wall adjacent to the boss 53, that is, the fiber bundle layer of
fibers or
2o fiber bundles which contact the boss 53 is thick, and the wall of a
shoulder portion
(which is adjacent to the boundary between one domed end portion and the
cylindrical portion) is thin. Thus, there are redundant fibers F adjacent to
each
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boss 53. This outcome becomes more significant as the ratio of the diameter of
the cylindrical portion to the diameter of the boss increases. In such a fiber
arrangement, the fibers are concentrated adjacent to each boss, with the
result
that it causes malformation and increases manufacturing costs due to the
redundant fibers.
To prevent fibers arranged at the domed end portions adjacent to the
bosses from being excessively thicker than those arranged at another portion
of
the domed end portions, as shown in FIG. 10, at the domed end portion 51 of
the
1o pressure vessel 50 on which fiber reinforced layer is formed by FW method,
fibers
F for reinforcement are wound to change a line adjacent to the pole to a line
around a lower latitude portion. This is disclosed, for example, in Japanese
unexamined patent publication No. 5-79598.
In the above publication, fibers F for reinforcement are impregnated with
epoxy resin and helically wound on the cylindrical body of the aluminum liner
with
a winding angle of 20 degrees. Then, the fibers F are wound so that the
winding
line deviates by a predetermined angle from an adjacent pole toward a lower
latitude portion. Additionally, the cylindrical portion 52 is wound by hoop
winding.
Japanese unexamined patent publication No. 2000-337594 discloses a
pressure vessel that eliminates redundant fibers which are concentrated
adjacent
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to the boss of each domed end portion, reducing the amount of fibers of the
vessel as a whole and making it easy to manufacture without side sliding of
fibers
during winding of the fibers. In the pressure vessel, the arrangement line of
the
fibers which form the shell that covers the liner at each domed end portion
includes two kinds of lines, one of which is in contact with the boss and the
other
of which is not in contact with the boss.
Fibers which pass a line in contact with the boss are wound by in-plane
winding. As shown in FIG. 11, the majority of the wound fibers 54 passing on a
line
1o which does not contact the boss 53 are arranged so as to pass near a
geodesic
line at the end of the cylindrical portion 52 through the helical winding 55,
which
gradually increases its arrangement angle and connects the hoop winding 56,
which is arranged at the cylindrical portion 52. The wound fibers 54 passing
on
the line which does not contact the boss 53 are arranged on a plane
perpendicular to tangential line L, which is in a plane including a vertex of
the
winding portion at the domed end portion 51 and the axis of the liner and also
passes a vertex of the winding portion.
However, when high-pressure gas (for example, 20 MPa or more) is
2o contained in the pressure vessel, it is more effective to increase the
amount of
fibers (fiber bundles) contributing to enhancing the strength of the pressure
vessel
in the axial direction which are arranged to pass on the boss by using helical
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winding or in-plane winding. When arranged as described above, the thickness
of
the fiber bundle layer adjacent to the boss increases in comparison to a
portion
adjacent to the cylindrical body of the liner.
In this case, when the fiber bundles are wound on the fiber bundle layer
which is thickly wound on the boss, problems occur such as sliding of the
fibers
and malformation, thereby causing an undesirable arrangement of fiber bundles
to pass on the boss. Additionally, the force pressing the precedently wound
(arranged) fiber bundles is weakened in the area ranging from the portion
1o adjacent to the boss to the shoulder portion of the pressure vessel.
To compensate the above weakness, more fiber bundles need to be
wound in the area (low latitude portion) ranging from the portion adjacent to
the
boss to the shoulder portion for shape correction. The fiber bundles wound at
this
15 area contribute little to enhance strength in the axial direction. An
increase in fiber
bundles wound at the domed end portion leads to extra fibers to be wound at
the
cylindrical portion. Accordingly, as the amount of fibers increases, the
outside
diameter of the cylindrical portion becomes larger.
2o The present invention is directed to providing a pressure vessel in which
the fibers that range from the portion adjacent to the boss of the pressure
vessel
to the shoulder portion which contribute little to enhancing the strength of
the
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pressure vessel in the axial direction are reduced and the amount of fibers
required for ensuring the same pressure resistance are reduced even if the
fiber
bundles wound at the domed end portion are arranged to pass on the boss.
SUMMARY
In accordance with the present invention, the pressure vessel has an
airtight liner and a shell. The shell made of fiber reinforced plastic is
formed by
curing resin impregnated fiber bundles wound outside of the liner. The
pressure
1o vessel has a cylindrical portion, a domed end portion on each end of the
cylindrical portion and a boss provided at the center of each domed end
portion.
The shell includes at least two fiber bundle layers which are formed by the
resin
impregnating fiber bundles and at least one shape correction member arranged
between the fiber bundle layers at each domed end portion.
In accordance with the present invention, a method for manufacturing a
pressure vessel having a cylindrical portion, a domed end portion on each end
of
the cylindrical portion and a boss provided at the center of the domed end
portion,
wherein resin impregnated fiber bundles are wound outside of an airtight liner
by
filament winding, includes: fixing the liner at a rotation support portion of
a
filament winding apparatus so as to rotate integrally therewith, performing
the
filament winding while an annular shape correction member is prepared at a
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saving position, which does not intertere the filament winding, between the
rotation support portion and the liner for adjusting a shape of a fiber bundle
layer
formed at the domed end portion, moving the shape correction member prepared
at the saving position to contact the fiber bundle layer wound by then in the
mid
course of winding the fiber bundles, and continuing the filament winding.
Other aspects and advantages of the invention will become apparent from
the following description, taken in conjunction with the accompanying
drawings,
illustrating by way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention that are believed to be novel are set
forth with particularity in the appended claims. The invention together with
objects
and advantages thereof, may best be understood by reference to the following
description of the presently preferred embodiments together with the
accompanying drawings in which:
FIG. 1 is a cross-sectional view of a pressure vessel according to a first
preferred embodiment;
FIG. 2A is a schematic view showing an arrangement of fiber bundles by
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helical winding;
FIG. ZB is a schematic view showing an arrangement of fiber bundles by
hoop winding;
FIG. 3 is a schematic view showing an arrangement (arrangement line) of
fiber bundles on a domed end portion by helical winding;
FIG. 4 is a schematic side view of a winding portion of a filament winding
apparatus (or an FW apparatus);
FIG. 5 is a schematic plan view of the FW apparatus;
FIG. 6 is a partial cross-sectional view of a pressure vessel according to a
second preferred embodiment of the present invention;
FIG. 7 is a backside view of a shape correction member according to an
alternative embodiment of the present invention;
2o FIG. 8 is a partial cross-sectional view of a pressure vessel according to
an alternative embodiment of the present invention;
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FIG. 9 is a schematic view showing an arrangement of fibers by in-plane
winding;
FIG. 10 is a schematic view showing an arrangement of fibers on the
domed end portion of a pressure vessel according to the prior art; and
FIG. 11 is a schematic view showing an arrangement of fibers by helical
winding according to another prior art disclosure.
to DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first preferred embodiment according to the present invention will now
be described with reference to FIGS. 1 through 5. FIG. 1 is a schematic
cross-sectional view of a pressure vessel 11. FIG. 2A is a schematic view
showing
15 an arrangement of fiber bundles by helical winding. FIG. 2B is a schematic
view
showing an arrangement of fiber bundles by hoop winding. FIG. 3 is a schematic
view showing an arrangement (arrangement line) of fiber bundles by helical
winding at a domed end portion 13 of the pressure vessel 11. FIG. 4 is a
schematic side view of a winding portion of a filament winding apparatus (or
FW
2o apparatus). FIG. 5 is a schematic plan view of the FW apparatus.
As shown in FIG. 1, the pressure vessel 11 is formed to have the domed
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end portion 13 at each end of the cylindrical portion 12, and has a boss 14 at
the
center of each domed end portion 13. The pressure vessel 11 includes an
airtight
liner 15 and a shell 16 made of fiber reinforced plastic (FRP), covering the
outside
of the liner 15.
The liner 15 has a cylindrical body 15a and a dome 15b on each end of
the body 15a, and has a boss 14 at the center of each dome 15b. When the
pressure vessel 11 is used as a hydrogen storage tank, the liner 15 is, for
example, made of aluminum alloy. The boss 14 has a threaded hole 14a for
io screwing a plug of a conduit or the like.
The shell 16 is formed so that resin-impregnated fiber bundles
(hereinafter, it may be simply referred to as fiber bundles) are wound outside
of
the liner 15 and then cured. In this embodiment, carbon fiber is used as a
reinforcement fiber of FRP and epoxy resin is used as a resin.
Each domed end portion 13 includes a shape correction member 18
between a first fiber bundle layer 17a, which is precedently wound, and a
second
fiber bundle layer 17b, which is subsequently wound. Namely, each shape
2o correction member 18 is interposed between the first fiber bundle layer 17a
and
the second fiber bundle layer 17b. The shape correction member 18 has a
smaller
outside diameter than the portion of the first fiber bundle layer 17a on the
body
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15a of the liner 15 and its outer surface has such a hardness that fiber
bundles
wound outside of the shape correction member 18 do not bite thereinto. The
shape correction member 18 has a hole at the center thereof. The hole has the
same or a slightly larger diameter as the first fiber bundle layer 17a
adjacent to
the boss 14. In this embodiment, the shape correction member 18 is made of
epoxy resin. The shape correction member 18 is formed so that the surface of
the
shape correction member 18 adjacent to the liner 15 is shaped so as to line
along
the surface of the first fiber bundle layer 17a and arranged to fill in a
recess 19 of
the surface in a cross-section of the pressure vessel 11 taken along the axis
to thereof. The shape correction member 18 has a convex surface on the side
opposite to the liner 15 and the curvature of the convex surface is smaller
than
that of the outer surface of the dome 15b of the liner 15. The portion of the
first
fiber bundle layer 17a adjacent to the boss 14 and the shoulder portion
thereof
are smoothly connected by a curved surface.
The fiber bundles which form the shell 16 are sequentially wound on the
outer surface of the liner 15 to form a fiber bundle layer with a
predetermined
thickness. The fiber bundles 20 include one wound by helical winding as shown
in
FIG. 2A and the other wound by hoop winding as shown in FIG. 213. Hoop winding
2o is made only along a portion on the body 15a.
The fiber bundles 20 which form the helical winding are arranged so that
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its arrangement line at the domed end portion 13 (or on the dome 15b) extends
along the tangential direction of the boss 14 as shown in FIG. 3 or slightly
winds
on the boss 14 as shown by the dotted line in FIG. 3. This depends on pressure
resistance required for the pressure vessel 11, however. The winding angle of
the
fiber bundles 20 which form the helical winding preferably, for example,
ranges
from 10 degrees to 25 degrees. The language "winding angle" means an angle
between the fiber bundles 20 and the axial direction on the cylindrical
portion 12.
The following will describe a method of manufacturing the pressure vessel
11. The FW apparatus is used for manufacturing the pressure vessel 11. As
shown in FIG. 4, the FW apparatus 31 has a pair of chucks 32 as a rotation
support portion for rotatably supporting a wound member such as a liner. As
shown in FIG. 5, the FW apparatus 31 has a fiber bundle feeder 33, a resin
impregnating apparatus 34, a fiber bundle guide 35 and a fiber bundle feeding
head 36. The fiber bundle feeding head 36 is movable longitudinally (in the
lateral
direction in FIG. 5) of the fiber bundle wound member (the liner 15 in this
embodiment) which is supported by the chucks 32. The fiber bundle feeding head
36 ties fiber bundles 20 fed from a plurality of bobbins B and shapes it into
a flat
ribbon to be wound outside of the liner 15.
A known structure is used for an actuator 37 for reciprocating the fiber
bundle feeding head 36, in which a ball screw is used and a movable body 37a,
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which is integrally movable with a nut, is moved in one axial direction. A
raising
and lowering actuator (not shown) is fixedly mounted on the movable body 37a,
and the fiber bundle feeding head 36 is mounted on the raising and lowering
actuator 37.
The fiber bundle feeder 33 is formed so that a plurality of bobbins B (three
in this embodiment), on which fiber bundles 20 are wound, are supported by
respective spindles 33a connected to a tension control (not shown). A powder
brake or a permanent torque which applies a load on the spindles 33a by over
1o current is, for example, used as a tension control. The fiber bundles 20
are, for
example, made of carbon fiber non-twisted multifilament, which has a filament
number of about 3000 through about 96000.
The resin impregnating apparatus 34 has a resin tank 34a and a
spreading roller 34b, and is provided with a roller (not shown) for guiding
fiber
bundles 20 which are drawn from the bobbins B to a predetermined position and
a
roller (not shown) for guiding fiber bundles 20, which are impregnated with
resin
in the resin tank 34a, above the resin tank 34a. The fiber bundle guide 35 has
a
guide portion (not shown) having the shape of the teeth of a comb for guiding
the
2o fiber bundles 20, which are drawn from a plurality of the bobbins B so as
to be
treated with resin impregnation separately.
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The chucks 32 rotatably support a fiber bundle wound member around the
axis of the member and are driven by a variable speed motor which is
controlled
by a controller (not shown). The moving speed of the fiber bundle feeding head
36
is made synchronous with the rotation of the variable speed motor. Thus, the
winding angle of the fiber bundles 20 to the fiber bundle wound member may be
set to an optional angle.
Then, the liner 15 is supported by the chucks 32 of the FW apparatus 31
so as to be rotated integrally therewith, and the shape correction members 18
are
1o prepared at their respective saving positions shown in FIG. 4, which do not
interfere with filament winding, between the chucks 32 and the liner 15. In
this
embodiment, a support member 39 for temporarily supporting the shape
correction member 18 extends over the chuck 32 from each side of the FW
apparatus 31 to a portion adjacent to the boss 14 of the liner 15, which is
supported by the chucks 32. The distal end portion 39a of each support member
39 is used as a saving position for the shape correction member 18. The shape
correction member 18 is supported so that it is hung at the distal end portion
39a
of the support member 39.
In this embodiment, the liner 15 is not directly supported at the bosses 14
by the chucks 32 but is supported through rods 38 by the chucks 32. Each rod
38
has a small-diameter external thread portion which is screwed into the
threaded
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hole 14a of the boss 14 at its distal end. The boss 14 is elongated so that
the
external thread portion is screwed into the boss 14 of the liner 15.
The operator draws fiber bundles 20 from the fiber bundle feeding portion
33, guides them to the fiber bundle feeding head 36 through the resin
impregnating apparatus 34, the fiber bundle guide 35, and the like, and then
fixes
the end of the fiber bundles 20 at a predetermined position of the liner 15
after the
fiber bundles 20 are inserted into the fiber bundle feeding head 36. Fixing
work of
the end of the fiber bundles 20 is manually performed by the operator, and,
for
1o example, performed by using adhesive tape. The operator inputs the rotation
speed during filament winding, the width of reciprocation during winding
operation
of the fiber bundle feeding head 36, and the like, to a controller (not
shown). The
filament winding is thus performed under such a situation.
The fiber bundles 20 are arranged by helical winding so as to be in
contact with the boss 14, and the wound positions are deviated for every
winding
on both domes 15b. The fiber bundles 20 are wound on the domes 15b until they
cover the entirety of the domes 15b. Thus, a single helical winding layer is
formed
on each dome 15b, while two helical winding layers are formed on the body 15a.
2o The hoop winding layer is formed on the body 15a with a predetermined
thickness.
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As a predetermined amount of fiber bundles is wound on the domes 15b
by helical winding, filament winding is interrupted, thus finishing winding of
the
first fiber bundle layer 17a. In this embodiment, the language "predetermined
amount" means that in the fiber bundle layer wound on the domes 15b the ratio
of
the thickness of the portion adjacent to the boss 14 to the thickness of a
portion
spaced apart from the boss 14 is so determined that, when the winding of the
fiber
bundles 20 is continued, the fiber bundles 20 will not be in contact with the
precedently wound fiber bundles 20 or contact with little pressure. This
predetermined amount is calculated by experiment in advance. In a state where
to the amount of helical winding has reached a predetermined amount, the
surface
of the first fiber bundle layer 17a is adjacent to the boss 14 and has a
rounded
shape which concaves inwardly to the liner 15 to form a recess 19 as seen in a
cross-section taken along the axis of the pressure vessel 11. As a result,
adjacent
to the boss 14, the fiber bundles 20 wound on the surface of the first fiber
bundle
layer 17a may not be in contact with the first fiber bundle layer 17a or may
contact
it with little contact pressure. it is noted that the thickness of the fiber
bundle layer
means the length of the fiber bundle layer in the direction perpendicular to
the
surface of the dome 15b.
2o The shape correction member 18, which is located at the saving position,
is moved along the rod 38 to be arranged at a position where it is in contact
with
the wound first fiber bundle layer 17a which has been wound by then. The shape
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correction member 18 has a surface adjacent to the liner 15, the surface being
shaped along the surface of the first fiber bundle layer 17a so as to fill the
recess
19. After that, the filament winding is continued, and the helical winding is
performed as described above to form the second fiber bundle layer 17b. Thus,
the second fiber bundle layer 17b has the required thickness for ensuring
desired
pressure resistance is formed, and the winding of fiber bundles 20 is
finished.
After the winding has finished, the wound body including the liner 15 is
removed from the FW apparatus 31 and then placed in a furnace for curing the
to resin at a predetermined temperature. Curing temperature varies for resin.
For
example, epoxy resin has a curing temperature of about 80 degrees C to 180
degrees C. The shell 16 made of FRP is formed by heat curing. After cooling
and
then removing the burr and the like, a plug and the like for filling with
hydrogen
and connecting an exhaust conduit is screwed into the threaded hole 14a of the
boss 14 thereby forming the pressure vessel 11.
When helical winding or in-plane winding is performed by filament winding
so that the arrangement line of the fiber bundles 20 wound outside of the
liner 15
having the domes 15b contacts the bosses 14 on the domes 15b, the portion
2o adjacent to the bosses 14 has a thicker fiber bundle layer than the portion
adjacent to the body 15a of the liner 15. As the amount of fiber bundle layer
wound on the domes 15b is increased, the rate of fiber bundles 20 adjacent to
the
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boss 14 increases, with the result that the surface of the fiber bundle layer
does
not have a rounded shape which convexes outwardly, as seen in a cross-section
taken along the axis of the pressure vessel 11, but has the recess 19 adjacent
to
each boss 14. Therefore, the fiber bundles 20 which are wound subsequently
press weakly against the fiber bundle layer which is wound (arranged)
precedently. However, in this embodiment, the shape correction member 18 is
arranged to fill in the recess 19, and the fiber bundles 20 wound outside of
the
shape correction member 18 has a rounded shape which convexes outwardly,
that is, spaced apart from the liner 15. Thus, the fiber bundles 20 are wound
to tightly around the domes 15b. As a result, the strength of the pressure
vessel 11
increases.
According to the preferred embodiment, the following advantages are
obtained.
(1 ) The pressure vessel 11 has a shell 16 made of fiber reinforced plastic
outside the airtight liner 15, including a cylindrical portion 12, domed end
portions
13 on both ends of the cylindrical portion 12, and a boss 14 provided at the
center
of each domed end portion 13. The shape correction member 18 is provided
2o between the first and second fiber bundle layers 17a, 17b at each domed end
portion 13. Accordingly, the fiber bundles which form the domed end portions
13
may further be arranged to pass on the bosses and wind tightly to sufficiently
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press the fiber bundles which are precedently wound (arranged). As a result,
even if the fiber bundles 20 wound at the domed end portions 13 are arranged
to
pass on the bosses 14, fibers that contribute little to increasing the
strength of the
pressure vessel 11 in the axial direction from the portion adjacent to the
bosses
14 to the shoulder portions may be reduced, and the amount of fibers required
for
ensuring the same pressure resistance may also be reduced. Thus, a light
weight
pressure vessel 11 and a thin-walled cylindrical portion 12 are achieved. The
thin-walled cylindrical portion 12 allows the pressure vessel to be compact.
io (2) The first and second fiber bundle layers 17a, 17b which form the domed
end portions 13 are formed only of the fiber bundles 20 which are wound in
contact with the bosses 14. Accordingly, all fiber bundles 20 which form the
domed end portions 13 efficiently contribute to increasing the strength of the
pressure vessel 11 in the axial direction.
(3) The shape correction member 18 has a surface adjacent to the liner 15,
the surface being shaped along the surface of the first fiber bundle layer
17a, and
arranged to fill in the recess 19 on the surface of the first fiber bundle
layer 17a.
Since the shape correction member 18 is arranged to fill in the surface of the
first
2o fiber bundle layer 17a, the fiber bundles 20 wound outside of the shape
correction
member 18 are arranged tightly along the surface opposite to the liner 15.
Thus,
the strength of the pressure vessel 11 is increased. During winding of the
fiber
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bundles 20 outside of the shape correction member 18, the inner precedently
wound fibers of the first fiber bundle layer 17a are tensed through the shape
correction member 18, and voids are prevented from being created in the
impregnated resin of the first fiber bundle layer 17a, thus contributing to
increasing the strength of the pressure vessel 11.
(4) The shape correction member 18 has a surface on the side opposite to
the liner 15, the surface having a smaller curvature than the outer surface of
the
dome 15b of the liner 15. In comparison to a structure in which the shape
1o correction member 18 has a surface on the side opposite to the liner 15,
the
surface having a greater curvature than the outer surface of the dome 15b of
the
liner 15, it is more appropriate to form (wind the fiber bundles 20) the domed
end
portions 13 of the pressure vessel 11.
(5) The shape correction member 18 has a smaller outside diameter than the
portion of the first fiber bundle layer 17a on the body 15a of the liner 15.
Accordingly, it is easy to wind the fiber bundles 20 outside of the shape
correction
member 18.
(6) Using the shape correction member 18 allows an arrangement line of the
fiber bundles 20 on the domes 15b to be estimated easily when the fiber
bundles
20 are to be further wound outside of the domes 15b that are already wound by
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the fiber bundles 20. Thus, design will be easier.
(7) During the manufacture of the pressure vessel 11, filament winding is
performed in a state where the liner 15 is fixed to the chucks 32 of the FW
apparatus 31 so as to rotate integrally therewith, and the annular shape
correction
members 18 for shape correction of the fiber bundle layer formed on the domes
15b are precedently prepared at saving positions, at which filament winding is
not
interrupted, between the chucks 32 and the liner 15. In the mid course of
winding
fiber bundles 20, the shape correction members 18 are prepared at the saving
to positions and are moved to positions to contact the first fiber bundle
layer 17a
which has been wound by then. Then, the filament winding is continued. When
the filament winding is interrupted and the shape correction members 18 are
moved to positions to contact the first fiber bundle layer 17a, the shape
correction
members 18 may be moved to appropriate positions on the first fiber bundle
layer
17a without removing the liner 15 from the chucks 32. Thus, arrangement of the
shape correction members 18 and continuation of the filament winding after the
arrangement are performed fast.
(8) Inserting of the shape correction members 18 improves the appearance
of the pressure vessel 11. Accordingly, the fiber bundles 20 for improving the
appearance are reduced thereby making the pressure vessel 11 light and
compact. Thus, fewer fiber bundles 20 are used to reduce manufacturing cost.
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(9) During supporting of the liner 15 by the chucks 32 of the FW apparatus 31,
the bosses 14 are not directly supported but rather supported through the rods
38
which are screwed into the threaded holes 14a. Since the length of the bosses
14
is determined as the sum of the length required for winding the fiber bundles
20
which form the domed end portions 13 and the length required for being
supported by the chucks 32, the pressure vessel 11 does not require additional
processes, such as removing an extra portion after the shell 16 is formed. In
addition, the liner 15 may be manufactured with less material.
(10) Since carbon fiber is used as the fiber bundle 20, and epoxy resin is
used
as a matrix resin, the pressure vessel 11 may be much lighter and more compact
while ensuring the strength for use as a fuel tank of an automobile.
The following will describe a second preferred embodiment of the present
invention with reference to FIG. 6. The second preferred embodiment differs
from
the first preferred embodiment in that a plurality of the shape correction
members
18 are arranged between the adjacent fiber bundle layers which form the domed
end portion 13. The other components are similar to those of the first
preferred
2o embodiment. The same reference numerals denote the substantially identical
components as those of the first preferred embodiment, and the description is
omitted. It is noted that in FIG. 6, to distinctly differentiate the first and
second
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fiber bundle layers 17a, 17b and the shape correction members 18, the
cross-section area of the shape correction members 18 is indicated not by
hatching but by dotting.
As shown in FIG. 6, the domed end portions 13 of the pressure vessel 13
each include three-layer first fiber bundle layers 17a, three shape correction
members 18 and an outer second fiber bundle layer 17b. Each shape correction
member 18 is made thinner than the shape correction member 18 of the first
preferred embodiment. The total thickness of the first and second fiber bundle
layers 17a, 17b depends upon the thickness of the used fiber bundle 20,
strength
of the fiber, pressure resistance required for the pressure vessel 11 and the
like. If
the total thickness of the first and second fiber bundle layers 17a, 17b for
ensuring
pressure resistance required for the pressure vessel 11 does not need to be so
thick, the single shape correction member 18 as well as the first preferred
embodiment may be enough.
However, if the total thickness of the first and second fiber bundle layers
17a, 17b needs to be thick, using the single shape correction member 18
results
in an excessive amount of fibers on the portion adjacent to the bosses 14,
even if
2o the shape of the winding of the fiber bundles 20 is corrected in such a
manner that
the winding of the fiber bundles 20 is interrupted in the mid course of the
filament
winding and the shape correction member 18 is arranged to contact the first
fiber
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CA 02525171 2005-11-O1
bundle layer 17a. As a result, the fiber bundles 20 contribute little to
increasing
the strength of the pressure vessel 11 in the axial direction in the same
amount of
winding, so that the amount of fiber bundles 20 for ensuring pressure
resistance
required for the pressure vessel 11 increases and the appearance of the domed
end portions 13 worsens. However, in this embodiment, a plurality of the shape
correction members 18 are used, so that the fiber bundles 20 may be wound for
effectively contributing to the strength of the pressure vessel 11 in the
axial
direction. Thus, the appearance of the domed end portions 13 gets better and
the
amount of fiber bundles 20 needed is reduced.
IO
According to the second preferred embodiment, in addition to the above
mentioned advantages, (1) through (10) of the first preferred embodiment, the
following advantage is obtained.
(11 ) A plurality of the shape correction members 18 are arranged between the
first and second fiber bundle layers 17a, 17b which form the domed end
portions
13. Accordingly, the domed end portions 13 may easily be formed in a desired
shape. Thus, design of the pressure vessel 11 will be easier and the
appearance
thereof will also be better. Furthermore, when the total thickness of the
first and
2o second fiber bundle layers 17a, 17b which form the domed end portions 13 is
made thicker for enhancing the strength of the pressure vessel 11, it permits
easy
adjustment of the thickness.
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CA 02525171 2005-11-O1
The present invention is not limited to the embodiments described above
but may be modified into the following alternative embodiments.
In an alternative embodiment, the shape of a surface of the shape
correction member 18 adjacent to the liner 15 is not limited to a smooth
shape.
For example, as shown in FiG. 7, a groove (recess) 18a may be formed to extend
radially. In this case, during the manufacture of the pressure vessel 11, the
shape
correction members 18 are prepared at positions in contact with the surface of
the
1o first fiber bundle layer 17a. Then, during winding of the fiber bundles 20
on the
shape correction members 18, resin liquid exuded from the first fiber bundle
layer
17a may easily be guided to the periphery of each shape correction member 18,
and, therefore, the shape correction members 18 easily closely contact the
surface of the first fiber bundle layer 17a.
In an alternative embodiment, as shown in FIG. 7, the shape correction
members 18 each have a through hole 18b. With the through holes 18b, during
the manufacture of the pressure vessel 11, after the shape correction members
18 are prepared at positions in contact with the surface of the first fiber
bundle
layer 17a, during winding of the fiber bundles 20 on the shape correction
members 18, resin liquid exuded from the first fiber bundle layer 17a may
easily
be drained outside from the shape correction members 18 through the through
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CA 02525171 2005-11-O1
holes 18b. Thus, the shape correction members 18 easily closely contact the
first
fiber bundle layer 17a. As shown in FIG. 7, the shape correction members 18
each may have a groove 18a and a through hole 18b.
In an alternative embodiment, the shape correction members 18 each
need not have a surface adjacent to the Liner 15 along the surface of the
first fiber
bundle layer 17a. Even if the shape correction members 18 each have a shape
that is partially spaced apart from the first fiber bundle layer 17a without
any
restriction, they are applicable when they are deformable so as to closely
contact
to the surface of the first fiber bundle layer 17a due to the tension of the
fiber
bundles 20 wound outside of the shape correction members 18.
In an alternative embodiment, the shape correction members 18 are not
limited to having a rounded surface on the side opposite to the liner 15, the
1~ curvature of the rounded surface being smaller than that of the outer
surface of
the dome 15b of the liner 15. The rounded surface may have a greater curvature
than the outer surface of the dome 15b. However, the rounded surface having a
smaller curvature than the outer surface of the dome 15b improves the
appearance of the domed end portions 13 and tends to cause appropriate tension
2o to act on the fiber bundles 20 during winding of the fiber bundles 20.
In an alternative embodiment, the material of the shape correction
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CA 02525171 2005-11-O1
member 18 is not limited to epoxy resin. For example, the shape correction
member 18 may be made of resin other than epoxy resin, such as fiber
reinforced
plastic, metal or ceramics. However, resin is preferable for reducing weight
in
comparison to metal and ceramics.
In an alternative embodiment, the shape correction members 18 each do
not have the same hardness as a whole, but may have a portion on the side
adjacent to the liner 15 which is softer than the other side thereof. For
example,
the shape correction members 18 each may have a two layer structure which
1o includes a first portion on the side opposite to the liner 15 and a second
portion on
the side adjacent to the liner 15, the first portion and the second portion
being
made of materials having difFerent hardness. For example, the shape correction
member 18 may have an elastomer layer on the side adjacent to the liner 15. in
this case, during the manufacture of the pressure vessel 11, in winding of the
fiber
bundles 20 on the shape correction member 18 on the side opposite to the liner
15, the shape correction member 18 easily closely contacts the first fiber
bundle
layer 17a, and voids between the shape correction member 18 and the first
fiber
bundle layer 17a are more difficult to create. As a result, the strength of
the
pressure vessel 11 is improved.
In an alternative embodiment, when the shape correction member 18 is
made of a heat curing resin such as epoxy resin, the hardness of the shape
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CA 02525171 2005-11-O1
correction member 18 may be different between the portion on the side adjacent
to the liner 15 and the portion on the side opposite to the liner 15 until the
heat
curing resin, which is impregnated in the fiber bundles 20, is heated and
cured
after the filament winding. In one example, the portion of the shape
correction
member 18 on the side opposite to the liner 15 is made of completely cured
heat
curing resin, while the portion on the side adjacent to the liner 15 is made
of the
same heat curing resin which is half cured. In this case, during the winding
of the
fiber bundles 20 on the portion of the shape correction member 18 on the side
opposite to the liner 15, the shape correction member 18 easily closely
contacts
to the first fiber bundle layer 17a on the side adjacent to the liner 15, and
voids
between the shape correction member 18 and the first fiber bundle layer 17a
are
difficult to create.
In an alternative embodiment, the shape correction member 18 is not
limited to one having a smaller diameter than a portion of the first fiber
bundle
layer 17a on the body 15a of the liner 15, but may have a greater diameter
than
the above portion. However, the shape correction member 18 having a smaller
diameter than the above portion is preferable.
2o In an alternative embodiment, the shape correction member 18 may be
formed of a plurality of rings (annular members) having different diameters.
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CA 02525171 2005-11-O1
In an alternative embodiment, the shape correction member 18 may be
formed so that a plurality of members are combined to be annular. In this
case,
during filament winding, even if the shape correction members 18 are not
precedently prepared at the saving positions between the chucks 32 of the FW
apparatus 31 and the liner 15, they may easily be arranged at the positions to
contact the surface of the first fiber bundle layer 17a.
In an alternative embodiment, the first and second fiber bundle layers 17a,
17b which form the domed end portions 13 are not limited to being formed only
by
1o helical winding but may be the combination of fiber bundle layer formed by
helical
winding and fiber bundle layer formed by in-plane winding, or may be formed
only
by in-plane winding. When the fiber bundles 20 are wound at the domed end
portions 13 so as to come in contact with the bosses 14, as the ratio of the
outside
diameter of the body 15a of the liner to the outside diameter of the boss 14
increases, the fiber bundle layer adjacent to the bosses 14 becomes thicker
than
the other portion. Accordingly, depending on the ratio of the outside diameter
of
the body 15a to the outside diameter of the boss 14 and pressure resistance
required for the pressure vessel 11, winding is appropriately determined for
the
fiber bundles 20 which form the domed end portions 13.
In the above preferred embodiments, in the first fiber bundle layer 17a
which forms the domed end portions 13, helical winding layer is first formed,
then
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CA 02525171 2005-11-O1
hoop winding layer is formed, and finally helical winding is formed again,
while the
second fiber bundle layer 17b is formed by helical winding. However, it is not
limited to this structure. The order of windings may be changed, another
winding
layer may be formed, and one helical winding layer of the first fiber bundle
layer
17a may be omitted. It is applicable that the winding layer of the fiber
bundles 20
which pass on the bosses 14 is contained in the fiber bundle layer adjacent to
the
shape correction member 18 on the side adjacent to the liner 15.
In an alternative embodiment, the fiber bundles 20 wound at the domed
1o end portions 13 are not limited to one all on the line passing the bosses
14. The
fiber bundles 20 wound at the domed end portions 13 may partially include low
latitude winding which does not pass on the bosses 14.
The shape correction members 18 are arranged between all three fiber
bundle layers in the second preferred embodiment but they are not limited to
this
arrangement. In an alternative embodiment, at least one shape correction
member 18 is arranged between the fiber bundle layers.
In an alternative embodiment, four or more fiber bundle layers may be
2o formed. In this case, the shape correction members 18 need not be arranged
between every adjacent fiber bundle layers. It is applicable that at least one
shape correction member 18 is arranged between the fiber bundle layers.
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CA 02525171 2005-11-O1
In an alternative embodiment, the pressure vessel 11 has a heat
exchanger inside the liner 15. When gas is filled in the pressure vessel 11
with
high pressure, the gas needs to be cooled to fill therein for a short time due
to
heat resulting from compression. Particularly, when the pressure vessel 11 is
used as a hydrogen storage tank and hydrogen storage material such as
hydrogen storing alloy is filled inside, the inside of the pressure vessel 11
needs
to be cooled. In this case, the heat exchanger is preferably mounted inside
the
liner 15. As shown in FIG. 8 showing the heat exchanger mounted inside the
liner
15, a cover 21 may be provided as the dome 15b of the liner 15. For example,
the
liner 15, separable on one end (which is shown in FIG. 8), includes an opening
23,
instead of the dome 15b of the preferred embodiment, and a cover 21. The
opening 23 has a larger diameter than the outside diameter of the heat
exchanger
22. The cover 21 covers the opening 23 and is integrally formed with the heat
exchanger 22. The cover 21 is fixed to the body 15a by screws 24. The heat
exchanger 22 has a heat medium conduit 25, an end plate 26, a heat transfer
fin
27 and a cylindrical filter 28, and a hydrogen storing alloy (not shown) is
filled
between the end plate 26 and the heat transfer fins 27.
2o In an alternative embodiment, when the pressure vessel 11 has a heat
exchanger inside the liner 15, the liner 15 need not be separable. For
example, a
heat exchanger is fixed to one dome 15b, and the other end is formed by a
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CA 02525171 2005-11-O1
drawing operation. After that, the shell 16 is formed by filament winding and
heat
curing.
In an alternative embodiment, the material of the liner 15 is not limited to
aluminum alloy but may be another metal such as stainless steel or copper or
may be airtight resin instead of metal. When the liner 15 is made of resin,
the
boss 14 made of metal is fixed to the center of the dome 15b. A liner made of
resin contributes to light weight in comparison to the liner 15 made of metal.
1o In an alternative embodiment, when the liner 15 is directly supported by
the chucks 32 of the FW apparatus 31, the boss 14 is elongated to make a
winding position for the fiber bundles 20 wound on the dome 15b instead of
supporting the pressure vessel 11 through the rod 38. Then, the liner 15 is
supported by the chucks 32 at the bosses 14, and an extra portion is cut off
or
removed after winding of the fiber bundles 20 and curing of the resin.
In an alternative embodiment, the matrix resin of FRP which forms the
shell 16 is not limited to epoxy resin but may be heat curing resin such as
polyimide resin or thermoplastic resin having a high elastic modulus in
bending
such as polyetheretherketone may be used in conformity with performance
required for the pressure vessel. Another resin such as vinyl ester resin and
phenolic resin may be used. In this case, the cost of these resins is lower
than
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CA 02525171 2005-11-O1
that of epoxy resin, so that manufacturing cost is reduced.
In an alternative embodiment, prepreg fiber in which carbon fibers are
precedently impregnated is used. In this case, no resin impregnating apparatus
is
needed, so that work time may be reduced and installation space of the entire
apparatus may be reduced by the space of resin impregnating apparatus.
In an alternative embodiment, the material of the fiber bundles 20 is not
limited to carbon fiber. Another inorganic fiber such as glass fiber or
organic fiber
to having a high strength and a high elasticity such as polyaramide is used in
conformity with performance required for the pressure vessel.
In an alternative embodiment, the body 15a of the liner 15 is not limited to
a cylindrical shape but may be elliptical in cross section or a polygonal in
shape. It
15 is noted that the fiber bundles 20 should be formed to be continuously
smoothly
wound on the body 15a and over the substantially hemispherical domes 15b.
In an alternative embodiment, ultraviolet curing resin is used as matrix
resin instead of heat curing resin.
Therefore, the present examples and embodiments are to be considered
as illustrative and not restrictive. The invention is not to be limited to the
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CA 02525171 2005-11-O1
embodiments described herein. It is to be understood that other similar
embodiments may be used or modifications and additions may be made to the
described embodiments for performing the same function. Therefore, the claimed
invention should not be limited to any single embodiment, but rather should be
construed in breadth and scope in accordance with the appended claims.
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