"PRESSURE VESSEL AND SUPPORT SYSTEM FOR A PRESSURE VESSEL"

[0001] The present invention relates to a support system for pressure vessels made of composite material and a new pressure vessel made of composite material.

[0002] The development of advanced composite materials allowed to manufacture lightweight pressure vessels made of composite overwrap material classified in different categories, among which, for example, type 4 indicates pressure vessels with an inner non- metal liner and an outer reinforcing composite layer containing fibers.

[0003] One of the crucial aspects when using pressure vessels made of composite overwrap material is their safe and space-saving support during transport and use.

[0004] When used as a fuel tank for a vehicle or for a similar application subject to movement and vibration, it is known to support the pressure vessel, e.g. a cylindrical gas cylinder with two ogive-shaped ends, by means of two metal bands extending around the circumference of the vessel and attached to a support frame ("rack") of the vehicle or of a similar application. Being the annular bands tightened directly around the reinforcing layer surrounding the cylindrical part of the gas cylinder, these are suitable for providing a constraint in the direction transverse to the longitudinal axis of the gas cylinder, but they do not satisfactorily reconcile the requirements of having to block the gas cylinder also against longitudinal movements while allowing longitudinal and transverse expansion of the gas cylinder due to the filling-emptying cycle.

[0005] Furthermore, in order to ensure an effective blockage of the gas cylinder on three axes, the bands must exert a clamping pressure on the surface of the cylinder which should be less than about 30N/cm ² in order not to deteriorate the carbon fiber layer. As a result, the bands reach such undesirably large widths as to prevent the visual inspection of the cylinders, increase the assembly and disassembly times and increase costs.

[0006] Finally, the presence of the fixing bands does not allow the positioning of the gas cylinders very close to one another and, therefore, maximal exploitation of the space available for gas storage purposes.

[0007] It is further known to support pressure vessels, e.g. cylindrical gas cylinders with two ogive-shaped ends, by means of fixing portions which surround two metal mouthpieces, each one arranged at either of the two ogive-shaped ends ("neck mounting"). The metal mouthpieces accommodate a vessel valve and are connected to the reinforcing layer and the inner liner to create a communication with the storage space inside the vessel.

[0008] The support of the pressure vessel by means of the two mouthpieces ("neck mounting") provides a reliable constraint both in the longitudinal direction and in the transverse direction and does not prevent longitudinal and radial expansion of the pressure vessel. In addition, the "neck mounting" allows quick assembly/disassembly of the gas cylinder to/from its support.

[0009] However, the vessel constrained at its ends acts as a swing beam and the mechanical stress, in particular vibration, is transmitted directly to the interface between the inner liner, typically made of plastic, and the metal mouthpiece, which constitutes the most critical area in terms of airtight sealing of the vessel. The deterioration of the airtight connection between the mouthpiece and the inner liner in pressure vessels supported at the mouthpieces is still an unsolved problem. Moreover, the presence of the fixing portions at the ends of the gas cylinders occupies a space of about 3 inches on each side of the cylinder and prevents a maximal exploitation of the occupied space for gas storage purposes.

[0010] Therefore, it is the object of the present invention to provide a new pressure vessel and a new support system for pressure vessels, having such features as to obviate at least some of the drawbacks of the prior art.

[0011] This and other objects are achieved by a pressure vessel having a gas-tight liner and a reinforcing layer made of composite material formed externally around the gas-tight liner, as well as a mouthpiece arranged on a mouthpiece side of the vessel and connected to the gas-tight liner and to the reinforcing layer for forming an opening of the vessel connectable to an outer conduit, wherein the pressure vessel comprises a connecting device having an anchoring portion arranged in the reinforcing layer and one or more connecting portions projecting from the anchoring portion outside the supporting layer on the same mouthpiece side but spaced from the mouthpiece.

[0012] Due to the presence of the one or more connecting portions projecting from the vessel on the mouthpiece side, it is possible to reduce the length of the mouthpiece itself and use the connecting portions, instead of the mouthpiece, for supporting the vessel. Thus, it is for example possible to position the valve at the mouthpiece on the same plane where, at a certain transverse distance from the mouthpiece, the support of the vessel by means of a coupling between the connecting portions and a support frame takes place. The result is a reduction of the total longitudinal dimensions for a given same working length of the gas storage space.

[0013] Moreover, the connecting device embedded in the reinforcing layer makes the pressure vessel more resistant to the so-called "DROP TEST", which consists in dropping the vessel onto the ogive in an axial direction or at a 45° angle with a kinetic energy of 488 Joules.

[0014] According to one aspect of the invention, the mouthpiece and the anchoring portion are made as separate pieces and connected to each other (preferably only) by means of the reinforcing layer.

[0015] Due to the separation between the mouthpiece and the anchoring portion, stresses and vibration transmitted between the vessel and a support frame are transmitted (at least predominantly) from the reinforcing layer through the connecting device to the support frame, bypassing the mouthpiece and the delicate connecting area between the mouthpiece and the inner liner.

[0016] According to a further aspect of the invention, the anchoring portion forms a ring extending around the mouthpiece.

[0017] This allows a concentric positioning of the connecting device with respect to the mouthpiece and with respect to a longitudinal axis of the vessel, and further allows to use the mouthpiece as a centering reference for the connecting device and as a support hub of the vessel while winding the fibers of the reinforcing layer above the anchoring portion.

[0018] According to a further aspect of the invention, the total contact area between the anchoring portion and the reinforcing layer is greater than the total contact area between the mouthpiece and the reinforcing layer. Furthermore, a possible contact area between the mouthpiece and the anchoring portion is smaller than both the total contact area between the anchoring portion and the reinforcing layer and the total contact area between the mouthpiece and the reinforcing layer.

[0019] This allows to use the mouthpiece as a reference for centering the anchoring portion while bypassing it when transmitting stresses and vibrations between the vessel and a support frame.

[0020] In order to better understand the invention and appreciate the advantages thereof, some exemplary, non-limiting embodiments will now be described with reference to the drawings, in which:

[0021] Figure 1 is a perspective view of a pressure vessel supported at its two opposite ends according to one embodiment of the invention,

[0022] Figure 2 is an enlarged view of a detail of the vessel in Figure 1 ,

[0023] Figure 3 is a partial radial-section view of the vessel according to one embodiment,

[0024] Figure 4 is a perspective view of a connecting device of the vessel according to one embodiment, [0025] Figure 5 is a radial-section view of the connecting device in Figure 4,

[0026] Figures 6, 7, 8 are front, side and perspective views of a support ring for support at the end of the pressure vessel according to one embodiment,

[0027] Figure 9 is a perspective view of a support clamp for support at the end of the pressure vessel according to one embodiment.

[0028] With reference to Figures 1 and 3, a pressure vessel 1 has a gas-tight liner 2 (typically the innermost layer of the wall 3 of the vessel 1 ) and a reinforcing layer 4 made of composite material, formed externally around the gas-tight liner 2, as well as at least one mouthpiece 5 arranged on a mouthpiece side of the vessel and connected to the gas-tight liner 2 and to the reinforcing layer 4 for forming an opening 6 of the pressure vessel 1 connectable to an outer conduit (not shown), where the pressure vessel 1 comprises a connecting device 7 having an anchoring portion 8 rigidly connected to the reinforcing layer, particularly arranged inside the reinforcing layer 4, and one or more connecting portions 9 projecting from the anchoring portion 8 outside the reinforcing layer 4 and the wall 3 of the vessel 1 on the same mouthpiece side but spaced from the mouthpiece 5 itself (Figure 3).

[0029] Due to the presence of the one or more connecting portions 9 projecting from the vessel 1 on the mouthpiece side, it is possible to reduce the length of the mouthpiece 5 itself and use the connecting portions 9, instead of the mouthpiece 5, for supporting the vessel 1 . Thus, it is for example possible to position a valve 10 at the mouthpiece 5 on the same plane where, at a certain transverse distance from the mouthpiece 5, the support of the vessel 1 by means of a coupling between the connecting portions 9 and a support frame 1 1 takes place. The result is a reduction of the total longitudinal dimensions with the same working length of the gas storage space.

[0030] According to one embodiment, the mouthpiece 5 and the anchoring portion 8 are made as separate pieces and rigidly connected to each other only by means of the reinforcing layer 4 (Figure 3).

[0031] Due to the separation between the mouthpiece 5 and the anchoring portion 8, the stresses and vibrations transmitted between the vessel 1 and the support frame 1 1 are transmitted from the reinforcing layer 4 through the connecting device 7 to the support frame 1 1 , bypassing the mouthpiece 5 and the delicate connecting area 12 between the mouthpiece 5 and the inner liner 2.

[0032] According to an embodiment, the anchoring portion 8 forms a ring extending around the mouthpiece 5 (Figure 3, 4). This allows a concentric positioning of the connecting device 7 with respect to the mouthpiece 5 and with respect to a longitudinal axis 18 of the vessel 1 (in the case of a pressure vessel 1 substantially cylindrical in shape with two opposite ogive-shaped or semi-sphere cap-shaped ends 19, 20), and further allows to use the mouthpiece 5 as a centering reference for the connecting device 7 and as a support hub of the vessel 1 while winding the fibers of the reinforcing layer 4 above the anchoring portion 8.

[0033] According to a further embodiment, the total contact area between the anchoring portion 8 and the reinforcing layer 4 is greater than the total contact area between the mouthpiece 5 and the reinforcing layer 4. Furthermore, a possible contact area (if provided) between the mouthpiece 5 and the anchoring portion 8 is preferably smaller than both the total contact area between the anchoring portion 8 and the reinforcing layer 4 and the total contact area between the mouthpiece 5 and the reinforcing layer 4.

[0034] This allows to use the mouthpiece 5 as a reference for centering the anchoring portion while bypassing the mouthpiece 5 when transmitting stresses between the vessel 1 and the support frame 1 1 .

[0035] According to an aspect of the invention, the connecting portion or portions 9 are initially separated from the anchoring portion 8 and subsequently coupled therewith, for example by screwing or interference or snap insertion. This allows to use the same anchoring portion 8 with different connecting portions 9 to adapt the connecting device 7 to different external support conditions. Similarly, it is possible to use different anchoring portions 8 with the same type of connecting portion 9 to adapt the connecting device 7 to pressure vessels 1 with different geometries or structural configurations.

[0036] According to one embodiment, the connecting device 7 may form one or more coupling interfaces, accessible from outside the vessel 1 with wall 3 (and in particular with the reinforcing layer 4) already completed, for a reversible coupling, for example by screwing, of an external element 13 of the connecting portion 9.

[0037] This allows a versatile coupling of the connecting device 7 not only during manufacture of the pressure vessel 1 , but also on the user side or in the event of a change of use of a used pressure vessel 1 .

[0038] According to a preferred embodiment, the rigid connection of the anchoring portion 8 to the reinforcing layer 4 is a connection where the anchoring portion 8 is completely embedded in and surrounded by the reinforcing layer 4, for example by resting the anchoring portion 8 onto an intermediate thickness of the reinforcing layer 4 not yet completed and then completing the reinforcing layer by further winding the same above the anchoring portion 8. [0039] Alternatively, the rigid connection of the anchoring portion 8 to the reinforcing layer 4 is a connection by gluing of the anchoring portion 8 to the reinforcing layer 4.

[0040] The rigid connection of the anchoring portion 8 to the reinforcing layer may further be achieved by direct rigid attachment, for example by direct screwing or blockage by means of further threaded means, of the anchoring portion 8 to the mouthpiece 5 which, in turn, is rigidly attached to the reinforcing layer 4. This embodiment is not preferred, because it does not obviate the problem of transmission of support stresses to the mouthpiece and to the connecting area between the mouthpiece and the inner liner. However, this embodiment may also contribute to an increase in the volume of gas storage for a given longitudinal dimension.

[0041] According to one embodiment (Figures 3, 4, 5), the anchoring portion 8 forms an annular shell with a central opening 14 suitable for the insertion of the anchoring portion 8 above the mouthpiece 5, a generally convex outer surface 15 and an opposite generally concave inner surface 16 to facilitate the shape adaptation between the anchoring portion 8 and the reinforcing layer 4 in the ogive-shaped or semi-sphere cap-shaped region of the vessel 1 .

[0042] In a central region 17, adjacent and extending around the central opening 14, the anchoring portion 8 can be flattened, preferably planar, to aid machining operations and assembly of the vessel.

[0043] In a connecting region 21 between the anchoring portion 8 and the connecting portion(s) 9 (in the example in Figures 3, 5 the connecting region 21 is radially external to the central region 17), the anchoring portion 8 can have a thickness (axial to the longitudinal axis 18) greater than its thickness in the remaining areas, especially greater than the thickness in the central region 17. This facilitates a rigid and strong and/or removable connection, such as by screwing, between the anchoring portion 8 and the connecting portion(s) 9. In addition, the variation in thickness of the anchoring portion 8 with maximum thickness close to the connecting portions 9 and reduced thickness close to the mouthpiece 5 promotes the transmission of stresses between the vessel 1 and the support frame 1 1 which bypasses the mouthpiece 5.

[0044] The anchoring portion 8 may be made of steel or other mechanically resistant and tenacious materials.

[0045] One or more interstices between the reinforcing layer (4) and the anchoring portion (8), for example due to shape incompatibility, may be filled with a polymeric filler, in particular with a denser and more viscous epoxy resin than the resin forming the matrix of the reinforcing layer 4.

[0046] The connecting portion or portions 9 may comprise a plurality of, for example four, pins/studs which may be preferably arranged at a constant angular pitch, on a circumference concentric with the mouthpiece 5 or with the longitudinal axis 18 of the vessel 1 and which may be oriented parallel to the mouthpiece 5 or to the longitudinal axis 18.

[0047] In a preferred, but not limiting, embodiment, the connecting pins 9 are arranged on a circumference whose diameter is between 90mm and 200mm, preferably between 120mm and 180mm, even more preferably about 150mm. These ranges of diametrical distance allow to reconcile the need for support of the pressure vessel 1 as close as possible to its ends 19, 20 and to its longitudinal axis 18 and the need to increase the distance of the support zone from the mouthpiece 5.

[0048] Advantageously, the radial distance between the radially outer surface of the mouthpiece 5 and the radially inner surface of the connecting portions 9 is in the range from 25mm to 40mm, preferably from 30mm to 35mm.

[0049] Alternatively, the connecting portion or portions 9 may comprise one or more cylindrical walls or cylindrical-segment-shaped walls, concentric with the mouthpiece 5 or to the longitudinal axis 18 of the vessel 1 .

[0050] The connecting portions 9 may be made of steel or other mechanically resistant and tenacious materials.

[0051] According to one embodiment, the connecting portions 9 have an elastomeric outer coating 22, preferably with a grooved outer profile, adapted to act as a vibration damper.

[0052] The connecting portions 9 may form threaded free ends 32 onto which screw nuts for blocking the connecting portions 9 may be tightened to corresponding connecting seats 23 of a support structure (Figures 2, 3).

[0053] Figures 2, 3, 6-9 illustrate details of a possible embodiment of the coupling of the vessel 1 according to the invention to a support frame 1 1 . The connecting portions are removably received, by the interposition of the elastomeric coating 22, in corresponding connecting seats 23 of a support ring 24 consisting of two half-rings 25 connectable to each other by two bolts 26. The support ring 24 forms a cylindrical outer surface 27 by which it is received in a corresponding cylindrical seat 28 of a clamp 29 which may also be closed and opened (Figure 9) to block and to release the support ring 24.

[0054] The cylindrical seat 28 of the clamp 29 may allow rotation of the support ring 24, its translation in the longitudinal direction and/or blockage of the support ring 24 in the longitudinal direction and in rotation, so that the constraints of the vessel 1 may be adjusted and achieved.

[0055] In one embodiment, the vessel 1 is supported in a first support zone close to its mouthpiece 5 by means of one of said connecting devices 7 as well as in at least a second area opposite or distant from the mouthpiece 5.

[0056] In the second support area, the vessel 1 may be supported by a further one of said connecting devices 7 at a further mouthpiece 30 of the vessel 1 .

[0057] In a typical and advantageous, but not limiting, example, the further mouthpiece 30 may be configured as described with reference to the mouthpiece 5 and it may be concentric to the longitudinal axis 18 and arranged at the opposite end of the vessel 1 with respect to the first mouthpiece 5.

[0058] Alternatively, in the second support zone, the vessel 1 may be supported by a further connecting device 7 at a shank 31 of the vessel 1 anchored in the reinforcing layer 4, but with no connection to the inner liner 2.

[0059] Alternatively, in the second support zone, the vessel 1 may be supported by direct connection to a shank 31 of the vessel 1 anchored in the reinforcing layer 4, but with no connection to the inner liner 2.

[0060] Alternatively, in the second support zone, the vessel 1 may be supported by a metal band 33 extending around a cylindrical portion of the vessel 1 . Both a replacement of the support at the second end of the vessel 1 by means of a support by means of a metal band and an additional support of the vessel 1 by means of a metal band.

[0061] In one embodiment, the mouthpiece 5 comprises a central tubular portion 34, preferably cylindrical, which creates a passage for pressurized fluid through the opening 6 of the vessel and forms a threaded seat 35 for screwing the valve 10 and, possibly, a metal sealing surface 36 (intrados of the tubular portion 34), against which one or more sealing rings (not shown) of the valve 10 abut, and which metal sealing surface 36 can be preferably smooth and cylindrical or smooth and truncated-cone shaped. From the tubular portion 34, a coupling flange 37 may project, e.g. having the shape of a singular or double annular disk, forming a seat for the connection of the mouthpiece 5 to the gas-tight liner 2 (Figure 3). The mouthpiece 5 consisting of the tubular portion 34 and the connecting flange 37 may be made in a single piece (Figure 3), for example by machining with chip removal, forging, moulding or combinations of these processing and forming processes, or in multiple pieces initially separated and then assembled together.

[0062] The further mouthpiece 30 may be provided and connected to the vessel as the mouthpiece 5, and the structure and interconnection features described with reference to the mouthpiece 5 shall also apply to the further mouthpiece 30 and are not repeated here for conciseness of description.

[0063] In one embodiment, the pressure vessel 1 comprises a shank 31 arranged on the opposite side of the mouthpiece 5 and possibly coaxial therewith (Figure 3). Similarly to the mouthpiece 5, the shank 31 comprises a central portion, preferably cylindrical, solid or tubular in shape, which however does not create a passage for pressurized fluid, but which may form a threaded seat 38 for screwing a safety bolt 39 to achieve an end-of-stroke surface in the longitudinal direction.

[0064] Similarly to the mouthpiece 5 and to the further mouthpiece 30, the shank 31 may also act as a centering means for the anchoring portion 8 of the connecting device 7 and/or as a support hub of the vessel 1 during winding the fibers of the reinforcing layer.

[0065] The mouthpiece 5, the further mouthpiece 30 and the shank 31 (if provided) are preferably made of metal material, e.g. steel.

[0066] The gas-tight liner 2 made of synthetic material may, for example, made of polyamide (PA6 or PA66), polyethylene (PE), high density polyethylene (HDPE), polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), or the like.

[0067] The gas-tight liner 2 may be attached to the reinforcing layer 4 by:

[0068] - blow moulding into a mould consisting of the reinforcing layer 4 with one or more optional intermediate layers and/or

[0069] - moulding of the gas-tight liner 2 (for example, by a mould different from the reinforcing layer 4) and subsequent winding of the reinforcement sheet 4 around the gas- tight liner 2.

[0070] The reinforcing layer 4 acts to resist the internal pressure exerted by the stored fluid and may be manufactured by winding filaments of continuous carbon or glass fibers impregnated with epoxy resin on the previously manufactured layer or gas-tight liner 2 or on a mandrel which is subsequently removed.

[0071] Preferably, the reinforcing fibers of the reinforcing layer 4 exhibit a tensile strength greater than 4500 Mpa, preferably from 4800 MPa to 5200 MPa and a modulus greater than 200 GPa, preferably from 200 to 250 GPa.

[0072] Advantageously, the reinforcing layer 4 comprises a (volumetric) content of reinforcement fibers in the range from 50 vol% to 70 vol%, preferably from 55 vol% to 65 vol%, even more preferably about 60 vol%, wherein the balance of the volume is formed by the matrix, which may be an epoxy resin or vinyl ester cured by heat treatment, for example heating to about 120° for a period of about five hours.

[0073] Around the reinforcing layer 4, a further outer protection layer 40 may be formed, for example a paint layer or a shock-resistant layer.

[0074] The thus manufactured and configured pressure vessel 1 may be used for example as a gas cylinder or as a pressure storage reservoir, for example in KERS (Kinetic Energy Recovery System) systems. The support system of the pressure vessel 1 and the pressure vessel 1 may be advantageously used on board road, rail, aeronautical and nautical vehicles, as well as in industrial and household installations.