Pressure vessel with an optimized outer composite structure

Abstract

The present invention relates to a pressure vessel (4, 4') comprising an internal fluid storage chamber (3) and an outer composite structure (20) having a thickness (T) including both helical layers (20a) and hoop layers (20b) of reinforcing fibers, where at least 20% of the total thickness of all helical layers (20a) is located within a 25% innermost thickness (T) of the outer composite structure (20). The internal fluid storage chamber (3) is defined by a liner (6) having a first dome-shaped longitudinal end (12) with a first intermediate portion (13). The pressure vessel (4, 4') further comprises a first dome reinforced shell (16) having a shape complementary to the shape of the first dome-shaped longitudinal end (12) and a first intermediate portion (13) thereof, the first dome reinforced shell (16) being fitted onto the liner (6) only on the first dome-shaped longitudinal end (12) and on the first intermediate portion (13) thereof.

Description

Technical Field

[0001] The present invention relates to a pressure vessel for a vehicle. More precisely, the present invention relates to a pressure vessel and a vehicle comprising such a pressure vessel.

Background Art

[0002] High-pressure vessels for vehicles generally comprise a hollow housing. This housing, also called a liner, has a substantially cylindrical shape with two domed longitudinal ends and is made of a plastic material or other material such as a metal (e.g., aluminum) that is selected for its low weight and low manufacturing cost. This housing is intended to store a pressurized gas, such as dihydrogen, used by a vehicle equipped with a pressure vessel for various functions such as a power source. The pressurized gas exerts a strong constraint on the inner surface of the housing, thereby compromising the integrity of the housing and potentially causing dangerous leaks, especially in the case of combustible gases such as dihydrogen.

[0003] To improve the mechanical properties of the housing, it is known to wind filaments made of reinforcing fibers, such as carbon fibers, over the entire outer surface of the housing. The filaments are embedded in a resin to facilitate winding and ensure that each part of the outer surface of the housing is covered.

[0004] For example, as disclosed in Patent Document 1, Patent Document 2, and Patent Document 3, it is known to form an outer composite structure by winding both a helical layer and a hoop layer of reinforcing fibers around the outer surface of the housing. To avoid excessive mechanical stress in the innermost layer of the outer composite structure at the boundary between the substantially cylindrical shape and the domed longitudinal ends of the housing when the pressure vessel contains a pressurized gas, it is known to increase the thickness of the helical layer. This solution is not satisfactory because it increases the weight of the pressure vessel.

[0005] Regarding the dome-shaped longitudinal end of the housing, it is known to manufacture a dome reinforcement part or a dome reinforcement shell that has a filament winding line independently of the housing, and in a subsequent step, the dome reinforcement shell is fitted onto the housing. Patent Document 4 presents an example of such a dome reinforcement shell. When using such a dome reinforcement shell, the innermost layer of the outer composite structure at the boundary between the substantially cylindrical shape of the housing and the dome-shaped longitudinal end is still subject to excessive mechanical stress when the pressure vessel contains gas under high pressure.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above, it is necessary to optimize the pressure vessel by maintaining good mechanical properties while reducing the amount of reinforcing fibers used.

Means for Solving the Problems

[0009] The present invention provides a pressure vessel comprising an internal fluid storage chamber and an outer composite structure that encloses or encapsulates the internal fluid storage, the outer composite structure having a thickness that includes both a helical layer and a hoop layer of reinforcing fibers, wherein at least 20% of the total thickness of all the helical layers is located within 25% of the innermost thickness of the outer composite structure, and preferably at least 30% of the total thickness of all the helical layers is located within 20% of the innermost thickness of the outer composite structure.

[0010] According to the present invention, the distribution of the helical layers in the outer composite structure thickness is optimized. In fact, compared to the prior art, by arranging at least 20% of the total thickness of all the helical layers within 25% of the innermost thickness of the outer composite structure, it is no longer necessary to increase the thickness of the outer composite structure, particularly the total thickness of all the helical layers, in order to reduce the mechanical stress in the innermost layer of the outer composite structure when the pressure vessel contains gas under high pressure. The benefits of the present invention become even more evident when at least 30% of the total thickness of all the helical layers is arranged within 20% of the innermost thickness of the outer composite structure. This reduces the amount of fiber used to manufacture the outer composite structure while still maintaining good mechanical properties. This enables the resulting pressure vessel to be lightweight. Further, in this case, the time required to wind the outer composite structure onto the liner is reduced, thus shortening the manufacturing time.

[0011] The expression "helical layer of reinforcing fibers" means a continuous filament of fibers arranged in a helical direction as a reinforcing part, i.e., at an angle between 5° and 85° with respect to the longitudinal axis of the pressure vessel.

[0012] The expression "hoop layer of reinforcing fibers" means a continuous filament of fibers arranged in a hoop direction as a reinforcing part, i.e., at an angle between 85° and 90° with respect to the longitudinal axis of the pressure vessel.

[0013] The expression "total thickness of all helical layers" means the thickness of the laminated structure of the layers formed by laminating all the helical layers of the outer composite structure.

[0014] The expression "innermost thickness of the outer composite structure thickness" means the thickness of the outer composite structure closest to the internal fluid storage chamber.

[0015] According to the present invention, the internal fluid storage chamber is defined by a liner, and the liner - a substantially cylindrical central portion having a first outer diameter D1 at a first longitudinal end; - a first domed longitudinal end having a base portion, and a first intermediate portion located between the substantially cylindrical central portion and the first domed longitudinal end and connecting the first longitudinal end of the substantially cylindrical central portion to the base portion of the first domed longitudinal end. The pressure vessel further comprises a first dome reinforcement shell having a shape complementary to the shape of the first domed longitudinal end and its first intermediate portion, and the first dome reinforcement shell is fitted onto the liner only on the first domed longitudinal end and its first intermediate portion.

[0016] The expression "substantially cylindrical central portion" means that the central portion appears cylindrical when viewed from its outer surface and generally forms a cylinder in space.

[0017] Due to the auxiliary shape of the first dome reinforcement shell, the mechanical properties of the pressure vessel are improved by strengthening the first domed longitudinal end and its first intermediate portion. In particular, inside the outer composite structure, especially inside the innermost thickness of the outer composite structure, mechanical stress is reduced. This makes it possible to reduce the fibers used in the manufacture of the outer composite structure while maintaining good mechanical properties. As a result, the weight of the resulting pressure vessel is reduced. Further, this makes it possible to shorten the manufacturing time because the time for winding the outer composite structure around the liner and the first dome reinforcement shell is shortened.

[0018] Preferably, the base portion has a second outer diameter D2, and the second outer diameter D2 is smaller than the first outer diameter D1. Accordingly, due to the difference in diameter between the first outer diameter D1 and the second outer diameter D2, an insertion region is formed in the first intermediate portion, whereby the first dome reinforcement shell is positioned on the same plane as the liner or does not protrude excessively, thereby avoiding excessive mechanical stress being applied to the inside of the outer composite structure at the point where the first dome reinforcement shell protrudes. In a preferred embodiment, the first outer diameter D1 and the second outer diameter D2 are such that the first dome reinforcement shell is positioned on the same plane as the liner. Accordingly, the outer surface of the pressure vessel is particularly smooth. This improves the attachment of the outer composite structure and reduces the level of mechanical stress within the pressure vessel.

[0019] In a preferred embodiment, the first dome reinforcement shell is positioned on the same plane as the liner, more preferably, the substantially cylindrical central portion of the liner. The first dome reinforcement shell avoids excessive mechanical stress being applied to the inside of the outer composite structure at the point where the first dome reinforcement shell is positioned on the same plane as the liner. Accordingly, the outer surface of the pressure vessel is particularly smooth. This improves the attachment of the outer composite structure and reduces the level of mechanical stress within the pressure vessel.

[0020] The expression "the first dome reinforcement shell is positioned on the same plane as the liner" means that the outer surface of the liner is geometrically integrated with the outer surface of the first dome reinforcement shell.

[0021] Preferably, the outer surface of the first dome reinforcement shell is positioned on the same plane as the outer surface of the substantially cylindrical central portion of the liner. Accordingly, since the outer surface of the first dome reinforcement shell is geometrically integrated with the outer surface of the substantially cylindrical central portion of the liner, the first dome reinforcement shell does not protrude from the first outer diameter D1 of the substantially cylindrical central portion of the liner. Accordingly, the outer surface of the pressure vessel is particularly smooth. This improves the attachment of the outer composite structure and reduces the level of mechanical stress within the pressure vessel.

[0022] In a preferred embodiment, the liner is a plastic liner made of a thermoplastic material. This enables the manufacture of Type IV pressure vessels.

[0023] In a preferred embodiment, the first domed longitudinal end of the liner has a domed outer shape portion with a lower concavity towards the internal fluid storage chamber than the domed outer shape portion having a geodesic dome outer shape portion.

[0024] A geodesic dome refers to a dome structure based on a network of great circles on the surface of a hemisphere. The geodesics intersect to form triangular elements that have local triangular rigidity and also distribute stress throughout the structure. The geodesic dome outer shape can be generated by the technique described in Non-Patent Document 1. The geodesic dome outer shape enables isotropic tension loading of filaments.

[0025] The term "isotropic tension" refers to the property of a fully wound pressure vessel in which each filament of the outer composite structure wound around the liner and the first dome reinforcement shell is subjected to a constant pressure at all points within its path. In this configuration, virtually all of the stress imposed on the vessel by the compressed internal fluid is borne by the filaments of the outer composite structure, and the stress borne by the liner is very small.

[0026] Preferably, the maximum distance between the domed outer shape portion of the first domed longitudinal end and the domed outer shape portion of the domed longitudinal end having a geodesic dome outer shape portion is between 0.1% and 5% of the first outer diameter, preferably between 0.5% and 2.5% of the first outer diameter. These values are suitable for the first domed longitudinal end, are easily implemented in the manufacture of the liner, and enable more appropriately reducing the stress within the outer composite structure that seals or encloses the liner and the first dome reinforcement shell. When the stress is reduced in this way, it becomes possible to reduce the composite structure used (i.e., reduce the material).

[0027] The first dome reinforcement shell has a shape complementary to the shape of the first dome-shaped longitudinal end of the liner. Therefore, the first dome reinforcement shell also has a dome outer shape portion with a lower concavity towards the internal fluid storage chamber than a dome reinforcement shell having a geodesic dome outer shape portion.

[0028] In a preferred embodiment, the first intermediate portion of the liner has an outer peripheral surface selected from the group consisting of a cylindrical shape, a frustoconical shape, a curved shape, and combinations thereof. Thus, the outer surface of the liner provided with the first dome reinforcement shell is particularly smooth. This improves the attachment of the outer composite structure and reduces the stress level within the pressure vessel.

[0029] Preferably, the outer peripheral surface of the first intermediate portion is a combination of a first frustoconical surface and a first cylindrical surface. Thus, the liner can be regarded as a stepped liner having a first tapered outer shoulder between a substantially cylindrical central portion and the first dome-shaped longitudinal end.

[0030] In a preferred embodiment, the first dome reinforcement shell is fabricated using at least one of the techniques selected from the group consisting of a winding technique, an overwrapping technique, a braiding technique, and a tape placement technique. Advantageously, the tape placement technique is a laser automated tape placement (also referred to as LATP) technique.

[0031] In a particularly preferred embodiment, the first dome reinforcement shell consists of windings of layers of a fiber-reinforced composite material fabricated using a winding technique.

[0032] In a preferred embodiment, the matrix of the fiber-reinforced composite material is selected from the group consisting of a thermosetting resin and a thermoplastic polymer. Preferably, the matrix of the fiber-reinforced composite material is a thermosetting resin.

[0033] A thermosetting resin is formed by mixing two or more reactive components that form a reactive thermosetting precursor, which reacts upon exposure to curing conditions (e.g., heat, UV, or other radiation, or simply by contacting each other) to form the thermosetting resin. The thermosetting resin must be fully cured to produce a high-performance composite. After curing, the thermosetting resin becomes solid and can no longer flow, so it can no longer be processed or reshaped. Examples of thermosetting resins include unsaturated polyester, epoxy, vinyl ester, polyurea, isocyanurate, and polyurethane resins. It is possible to produce a thermosetting prepreg made of fibers impregnated with a reactive resin that has adhesiveness but is only partially cured so as to still be soft. This prepreg can be stored and later further processed under pressure by heating or exposing the resin to UV to complete the curing and solidification of the prepreg.

[0034] Thermoplastic polymers can change from a solid state (or non-flowing state) to a liquid state (or flowing state) and from a liquid state to a solid state by raising or lowering the temperature respectively. In the case of semi-crystalline polymers, when the temperature of the thermoplastic material is lowered, crystals are formed and the thermoplastic material solidifies. Conversely, when a semi-crystalline polymer is heated to a temperature above its melting point, the crystals melt and the thermoplastic material can flow. Examples of semi-crystalline thermoplastic materials include polyether ketones such as PEEK, PEKK, PEKKEK, polyamides such as PA6, PA66, PA10, PA11, PA12, and polyolefins such as PE, PP, etc. Amorphous thermoplastic materials do not form crystals and do not have a melting point. Amorphous thermoplastic materials solidify or have fluidity depending on whether the material temperature is above or below its glass transition temperature. Examples of amorphous thermoplastic materials include PEI, PSU, PES, PC, PS, TPU, etc. Therefore, both semi-crystalline and amorphous thermoplastic materials can be reshaped by heating them to a temperature above their melting point or glass transition temperature, and can be frozen into a new shape by lowering the temperature according to the melting point or glass transition temperature. Although not strictly correct from a physical perspective, for simplicity of explanation, both semi-crystalline and amorphous thermoplastic materials in the liquid state are referred to herein as "thermoplastic melts".

[0035] In a preferred embodiment, the fibers of the fiber-reinforced composite material are fibers selected from the group consisting of carbon fibers, aramid fibers, and glass fibers. This enables an appropriate balance between weight reduction and mechanical strength of the fiber-reinforced composite material. More preferably, the fibers of the fiber-reinforced composite material are carbon fibers.

[0036] In a preferred embodiment, the fibers of the fiber-reinforced composite material used to fabricate the first dome reinforcement shell are continuous fibers having a high elastic modulus, for example, 250 GPa. This further improves the mechanical strength of the fiber-reinforced composite material.

[0037] In a preferred embodiment, the liner is - The third outer diameter at the second longitudinal end, which is on the axially opposite side of the first longitudinal end of the substantially cylindrical central portion, and - A second domed longitudinal end having a base portion, preferably a fourth outer diameter, wherein the fourth outer diameter is smaller than the third outer diameter, the second domed longitudinal end being located between the substantially cylindrical central portion and the base portion, and further comprising a second intermediate portion connecting the second longitudinal end of the substantially cylindrical central portion to the base portion of the second domed longitudinal end. The pressure vessel further comprises a second dome reinforcement shell having a shape complementary to the shape of the second domed longitudinal end and its second intermediate portion, and the second dome reinforcement shell is fitted onto the liner only on the second domed longitudinal end and its second intermediate portion.

[0038] In this configuration, each longitudinal end of the substantially cylindrical central portion of the liner has a domed longitudinal end that exhibits advantageous mechanical properties of the present invention.

[0039] In a preferred embodiment, the second dome reinforcement shell is located in the same plane as the liner, more preferably, the substantially cylindrical central portion of the liner.

[0040] Preferably, the outer surface of the second dome reinforcement shell is located in the same plane as the outer surface of the substantially cylindrical central portion of the liner.

[0041] In a preferred embodiment, the second domed longitudinal end of the liner has a dome outer portion with a lower concavity towards the internal fluid storage chamber than the dome outer portion having a geodic dome outer portion.

[0042] Preferably, the maximum distance between the dome outer shape portion of the second dome-shaped longitudinal end portion and the dome outer shape portion of the dome-shaped longitudinal end portion having the geodesic dome outer shape portion is between 0.1% and 5% of the third outer diameter, preferably between 0.5% and 2.5% of the third outer diameter. These values are suitable for the second dome-shaped longitudinal end portion, are easily implemented in the manufacture of the liner, and make it possible to more appropriately reduce the stress in the outer composite structure that seals or encloses the liner and the second dome reinforcement shell. When the stress is reduced in this way, it becomes possible to reduce the composite structure used.

[0043] Since the second dome reinforcement shell has a shape complementary to the shape of the second dome-shaped longitudinal end portion of the liner, the second dome reinforcement shell also has a dome outer shape portion with a lower concavity towards the internal fluid storage chamber than the dome reinforcement shell having the geodesic dome outer shape portion.

[0044] Advantageously, the third outer diameter is approximately equal to the first outer diameter D1.

[0045] Preferably, the fourth outer diameter is approximately equal to the second outer diameter D2.

[0046] Advantageously, the second intermediate portion of the liner has an outer peripheral surface selected from the group consisting of a cylindrical shape, a frustum of a cone shape, a curved shape, and combinations thereof. Thus, the outer surface of the liner provided with the second reinforcement shell is particularly smooth. This improves the attachment of the outer composite structure and reduces the stress level in the pressure vessel.

[0047] Preferably, the outer peripheral surface of the second intermediate portion is a combination of a second frustum of a cone surface and a second cylindrical surface. Thus, the liner can be regarded as a stepped liner having a second tapered outer shoulder between a substantially cylindrical central portion and the second dome-shaped longitudinal end portion.

[0048] In a preferred embodiment, the second dome reinforcement shell is fabricated using at least one of the techniques selected from the group consisting of a winding technique, an exterior technique, a braiding technique, and a tape placement technique. Advantageously, the tape placement technique is a laser automated tape placement (LATP) technique.

[0049] In a particularly preferred embodiment, the second dome reinforcement shell consists of windings of layers of fiber-reinforced composite material fabricated using a winding technique.

[0050] In a preferred embodiment, a glass fiber layer may be provided on the outer composite structure to protect the helical layer and hoop layer reinforcing fibers of the reinforcing fibers.

[0051] Preferably, the reinforcing fibers are carbon fibers.

[0052] The present invention further relates to a vehicle comprising a pressure vessel according to the present invention.

Brief Description of the Drawings

[0053]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0054] The present invention will be described with reference to several drawings regarding specific embodiments. However, the present invention is not limited to the embodiments and the drawings, but is limited only by the claims. The drawings to be described are only schematic and non-limiting. In the drawings, the sizes of some elements may be exaggerated and may not be drawn to scale for illustrative purposes. Dimensions and relative dimensions do not correspond to actual reductions for implementing the present invention.

[0055] It should be noted that the term "comprising" used in the claims should not be construed as being limited to the means recited thereafter, and does not exclude other elements or steps. Therefore, this term should be construed as referring to the presence of the referenced and described features, integers, steps, or components, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Therefore, the scope of the expression "a device comprising means A and means B" should not be limited to a device consisting only of components A and B. This expression means, with respect to the present invention, that the relevant components of the device are only A and B.

[0056] FIG. 1 represents a vehicle 2 comprising pressure vessels 4, 4' configured to contain gas under high pressure. For example, the pressure vessels 4, 4' may contain dihydrogen for driving a fuel cell of the vehicle. The expression "pressure vessel" is intended to store gas under pressure and means a container capable of withstanding an internal pressure of up to 700 bar. For example, the pressure vessel may comply with Addendum 133 - Regulation No. 134 of the "Agreement Concerning the Adoption of Uniform Technical Prescriptions for Wheeled Vehicles, Equipment and Parts which can be Fitted and / or be Used on Wheeled Vehicles and the Conditions for Reciprocal Recognition of Approvals Granted on the Basis of these Prescriptions" issued by the United Nations.

[0057] FIG. 2 shows half of the pressure vessel 4 according to the first embodiment of the present invention. The pressure vessel 4 comprises an internal fluid storage chamber 3 defined by a liner 6. The liner 6 comprises a generally cylindrical central portion 8 extending along the longitudinal axis 10 and two similar dome-shaped longitudinal ends, namely a first dome-shaped longitudinal end 12 and a second dome-shaped longitudinal end. For the two similar dome-shaped longitudinal ends, only the first dome-shaped longitudinal end 12 is shown in FIG. 2. The liner 6 has a plane of symmetry that is perpendicular to the longitudinal axis 10 and passes through the center of the volume of the liner 6. In other embodiments, the liner 6 may have only one dome-shaped longitudinal end 12.

[0058] Since it has been found that for each pair of elements, the second element can be estimated by symmetry with respect to the plane of symmetry, only the first element will be described below.

[0059] The generally cylindrical central portion 8 has a first outer diameter D1 at the first longitudinal end 8a of the liner 6. The first domed longitudinal end 12 has a central axis coaxial with the longitudinal axis 10 and a base portion 12a of a second outer diameter D2. D2 is smaller than D1. The liner 6, more precisely, the first domed longitudinal end 12 further comprises a first intermediate portion 13 located between the generally cylindrical central portion 8 and the base portion 12a. The first intermediate portion 13 connects the first longitudinal end 8a of the generally cylindrical central portion 8 to the base portion 12a of the first domed longitudinal end 12.

[0060] The pressure vessel 4 comprises an outer composite structure 20 that seals or encloses both the liner 6 and the first dome reinforcement shell 16. The outer composite structure 20 comprises a domed portion 21 having a base portion 21a. The first dome reinforcement shell 16 has a shape complementary to the shape of the first domed longitudinal end 12 and its first intermediate portion 13. The first dome reinforcement shell 16 is fitted onto the liner 6 only over the first domed longitudinal end 12 and its first intermediate portion 13. In fact, the difference in diameter between the first outer diameter D1 and the second outer diameter D2 is such that an insertion region in the form of a first tapered outer shoulder is formed in the first intermediate portion 13 so that the first dome reinforcement shell 16 is located in the same plane as the liner 6. At this position, the first tapered outer shoulder houses the tip 27 of the first dome reinforcement shell 16. Thus, the first dome reinforcement shell 16 is located in the same plane as the liner 6, more preferably, the generally cylindrical central portion 8 of the liner 6. More precisely, the outer surface of the first dome reinforcement shell 16 is located in the same plane as the outer surface of the generally cylindrical central portion 8 of the liner 6.

[0061] Advantageously, the first domed longitudinal end 12 of the liner 6 has a domed outer profile portion 12b with a lower concavity towards the internal fluid storage chamber 3 than a domed longitudinal end with a geodesic dome outer profile portion.

[0062] Preferably, the maximum distance between the domed outer profile portion 12b of the first domed longitudinal end 12 and the domed outer profile portion of the domed longitudinal end with a geodesic dome outer profile portion is between 0.1% and 5% of the first outer diameter D1, preferably between 0.5% and 2.5% of the first outer diameter D1.

[0063] Since the first domed reinforcement shell 16 has a shape complementary to the shape of the first domed longitudinal end 12 of the liner 6, the first domed reinforcement shell 16 also has a domed outer profile portion with a lower concavity towards the internal fluid storage chamber 3 than a domed reinforcement shell with a geodesic dome outer profile portion.

[0064] In the present embodiment, the first intermediate portion 13 of the liner 6 has an outer peripheral surface composed of a combination of the first frustoconical surface 9 and the first cylindrical surface 11.

[0065] The pressure vessel 4 includes a boss 14 for injecting fluid into and discharging fluid from the liner 6. The boss 14 is fitted into a hole located in the first domed longitudinal end 12 of the liner 6 on the axially opposite side of the base portion 12a.

[0066] The first dome reinforcement shell 16 consists of windings of layers of fiber-reinforced composite material. For the fiber-reinforced composite material, it may be pre-impregnated and cured after being combined, or not pre-impregnated and impregnated, for example, by a resin injection process or generally a resin transfer molding process called the RTM process. During such a process, the curing of the composite material takes place while the composite material remains inside the resin injection tool or the resin transfer mold. It should be noted that the RTM process enables obtaining a particularly smooth outer surface of the first dome reinforcement shell 16 while reducing internal stresses. The first dome reinforcement shell 16 has a base portion 22a and a dome-shaped portion 22 including a central axis coaxial with the longitudinal axis 10 of the liner 6. The fibers of the fiber-reinforced composite material are selected from the group consisting of carbon fibers, aramid fibers, and glass fibers. Preferably, the fibers of the fiber-reinforced composite material are carbon fibers.

[0067] Furthermore, in order to protect the reinforcing fibers of the helical layer 20a and the hoop layer 20b of the reinforcing fibers, a glass fiber layer may be provided on the outer composite structure 20.

[0068] FIG. 3 shows a detailed view of the portion indicated by F in FIG. 2. The outer composite structure 20 of the pressure vessel according to the present invention has a thickness T including both a helical layer 20a and a hoop layer 20b of reinforcing fibers, and at least 20% of the total thickness of all the helical layers 20a is located within 25% of the innermost thickness T of the outer composite structure 20. In this embodiment, the reinforcing fibers are carbon fibers. Preferably, at least 30% of the total thickness of all the helical layers 20a is located within 20% of the innermost thickness T of the outer composite structure 20. In this embodiment, the outer composite structure 20 comprises 15 layers, namely, 9 helical layers 20a and 6 hoop layers 20b.

[0069] Figure 4 shows simulation results by the ABAQUS 2017 software combined with the Wound Composite Modeler (also called WCM) for ABAQUS 2017 that compares different stresses within the outer composite structure 20 that seals or encloses both the liner 6 and the dome reinforcement shell 16. The stress comparison is carried out in a portion between a distance of zero and a distance of 21a' from the center of the volume of the liner 6 in the first helical layer of the nine helical layers 20a of the outer composite structure 20. The distance of zero corresponds to the axial position of the center of the volume of the liner 6 along the longitudinal axis 10, and the distance 21a' corresponds to the axial position of the base portion 21a along the longitudinal axis 10 of the pressure vessel.

[0070] In this latter figure, the continuous line 28 indicates that when less than 20% of the total thickness of all nine helical layers 20a is located within the 25% innermost thickness T of the outer composite structure 20, the internal stress within the first helical layer of the outer composite structure 20 can reach 3500 MPa or more in the region of the first intermediate portion 13 near the base portion 21a. The short dashed line 29 indicates that when at least 20% of the total thickness of all nine helical layers 20a is located within the 25% innermost thickness T of the outer composite structure 20, the internal stress within the first helical layer of the outer composite structure 20 is below 3500 MPa in the region of the first intermediate portion 13 near the base portion 21a. The long dashed line 30 indicates that when at least 30% of the total thickness of all nine helical layers 20a is located within the 20% innermost thickness T of the outer composite structure 20, the internal stress within the first helical layer of the outer composite structure 20 is below 2500 MPa in the region of the first intermediate portion 13 near the base portion 21a. In this simulation, the internal stress within the first helical layer of the outer composite structure 20 is actually the membrane stress in the direction of the fibers of the first helical layer of the outer composite structure 20.

[0071] It can be seen from the latter figure that the internal stress within the first helical layer of the outer composite structure 20 can be significantly reduced by positioning more helical layers 20a within the innermost thickness T of the outer composite structure 20.

[0072] FIG. 5 shows a modified embodiment of the present invention. In this embodiment, the pressure vessel 4' is different from the pressure vessel 4 in that the first intermediate portion 13 of the liner 6 has an outer peripheral surface formed of a curved surface.

[0073] The pressure vessel of the present invention is already known in the art and may be manufactured by means not further described herein.

Explanation of reference numerals

[0074] 2 Vehicle 3 Internal fluid storage chamber 4, 4' Pressure vessel 6 Liner 8 Substantially cylindrical central portion 8a First longitudinal end 9 First frustoconical surface 10 Longitudinal axis 11 First cylindrical surface 12 First domed longitudinal end of the liner 12a Base portion of the first domed longitudinal end 12b Dome outer shape portion of the first domed longitudinal end 13 First intermediate portion 14 Boss 16 First dome reinforcement shell 20 Outer composite structure 20a Helical layer 20b Hoop layer 21 Dome-shaped portion of the outer composite structure 21a Base portion of the dome-shaped portion of the outer composite structure 21a' Second axial position 22 Dome-shaped portion of the first dome reinforcement shell 22a Base portion of the dome-shaped portion of the first dome reinforcement shell 27 Tip of the first dome reinforcement shell 28 Continuous line 29 Short dashed line 30 Long dashed line

Claims

**Claim 1** A pressure vessel (4, 4'), comprising: an internal fluid storage chamber (3); and an outer composite structure (20) that seals or encloses the internal fluid storage chamber (3), wherein the outer composite structure (20) has a portion having a thickness (T) that includes both a helical layer (20a) and a hoop layer (20b) of reinforcing fibers, and at the portion having the thickness (T) that includes both the helical layer (20a) and the hoop layer (20b), at least 20% of the total thickness of all the helical layers (20a) is located within 25% of the innermost thickness (T) of the outer composite structure (20); wherein the internal fluid storage chamber (3) is defined by a liner (6), and the liner (6) comprises: a generally cylindrical central portion (8) having a first outer diameter D1 at a first longitudinal end (8a); a first domed longitudinal end (12) having a base portion (12a); and a first intermediate portion (13) located between the generally cylindrical central portion (8) and the base portion (12a) and connecting the first longitudinal end (8a) of the generally cylindrical central portion (8) to the base portion (12a) of the first domed longitudinal end (12), in the pressure vessel (4, 4'); the pressure vessel further comprising a first dome reinforcement shell (16) having a shape complementary to the shape of the first domed longitudinal end (12) and its first intermediate portion (13), the first dome reinforcement shell (16) being fitted onto the liner (6) only on the first domed longitudinal end (12) and its first intermediate portion (13), characterized in that, the pressure vessel (4, 4'). **Claim 2** The pressure vessel according to claim 1, wherein the first dome reinforcement shell (16) is located in the same plane as the liner (6). **Claim 3** The pressure vessel according to any one of claims 1 and 2, wherein at the portion having the thickness (T) that includes both the helical layer (20a) and the hoop layer (20b), at least 30% of the total thickness of all the helical layers (20a) is located within 20% of the innermost thickness (T) of the outer composite structure (20). **Claim 4** The pressure vessel according to any one of claims 1 to 3, wherein the base portion (12a) has a second outer diameter D2, and the second outer diameter D2 is smaller than the first outer diameter D1. **Claim 5** The first domed longitudinal end portion (12) of the liner (6) has a dome outer shape portion (12b) with a lower concavity towards the internal fluid storage chamber (3) than a domed longitudinal end portion having a geodesic dome outer shape portion, the pressure vessel according to any one of claims 1 to 4.

6. The maximum distance between the dome outer shape portion (12b) of the first domed longitudinal end portion (12) and the dome outer shape portion of the domed longitudinal end portion having a geodesic dome outer shape portion is included between 0.1% and 5% of the first outer diameter D1, the pressure vessel according to claim 5.

7. The first dome reinforcing shell (16) has a dome outer shape portion with a lower concavity towards the internal fluid storage chamber (3) than a dome reinforcing shell having a geodesic dome outer shape portion, the pressure vessel according to any one of claims 1 to 6.

8. The first intermediate portion (13) of the liner (6) has an outer peripheral surface selected from the group consisting of a cylindrical shape, a frustum of a cone shape, a curved shape, and combinations thereof, the pressure vessel according to any one of claims 1 to 7.

9. The outer peripheral surface of the first intermediate portion (13) is a combination of a first frustum of a cone surface (9) and a first cylindrical surface (11), the pressure vessel according to claim 8.

10. The first dome reinforcing shell consists of a winding of layers of a fiber-reinforced composite material, the pressure vessel according to any one of claims 1 to 9.

11. The liner (6) is at a third outer diameter at a second longitudinal end portion on the axially opposite side of the first longitudinal end portion (8a) of the substantially cylindrical central portion (8), a second domed longitudinal end portion having a base portion, and a second intermediate portion located between the substantially cylindrical central portion (8) and the base portion and connecting the second longitudinal end portion of the substantially cylindrical central portion (8) to the base portion of the second domed longitudinal end portion, the pressure vessel further comprises a second dome reinforcing shell having a shape complementary to the shape of the second domed longitudinal end portion and its second intermediate portion, the second dome reinforcing shell being fitted onto the liner (6) only on the second domed longitudinal end portion and its second intermediate portion, the pressure vessel according to any one of claims 1 to 10.

12. A vehicle (2) comprising a pressure vessel (4, 4') according to any one of claims 1 to 11.

Images