High-pressure tank jacket and method for its manufacture

Abstract

Method for producing a jacket (10) for a high-pressure tank for obtaining the jacket (10) for the high-pressure tank by joining two jacket components (12, 14) made of plastic material, wherein the shell components (12, 14) are elements each including a flange element (20) provided near an open end (16) and including a bottom portion (22) projecting outwardly in a diametrical direction and a side portion (24) bent from the bottom portion (22) to one side of a closed end (18), an annular recess (26) being defined by the bottom portion (22) and the side portion (24), wherein the method for producing a jacket (10) for the high-pressure tank comprises: a contact step of arranging end surfaces of the open ends (16) of the two sheath members (12, 14) in contact with each other; a joining step for joining the end faces of the open ends (16) together by welding, and thereby obtaining a joint (46); and a cutting step for cutting the floor sections (22) and the side sections (24) of the flange elements (20) such that parts of the bottom sections (22) remain, wherein the flange elements (20) remain with a projection amount (L2), whereby a connection strength of the connection (46) becomes greater than or equal to a tensile strength of the plastic material.

Description

Technical field

[0001] The present invention relates to a shell for a high-pressure tank (high-pressure tank shell), which is a base portion of the high-pressure tank, and a method for manufacturing the same. Technical background

[0002] A high-pressure tank is provided, for example, in a fuel cell system and stores hydrogen gas that is supplied to anodes. This type of high-pressure tank includes a plastic shell made of a thermoplastic material or the like that has a hydrogen barrier property. This type of plastic shell is manufactured, for example, by bonding shell components of substantially identical shape to each other.

[0003] Specifically, the sheath components are each formed of a semi-cylindrical body, one end of which is an open end and the other end of which is a closed end that is gradually curved to converge. Furthermore, end surfaces of the open ends are supported against each other (brought into contact with each other), and then the end surfaces are bonded together. In a conventional technique disclosed in JP 2013-119924 A, this bonding is performed by laser welding.

[0004] The resulting plastic shell is then covered with a reinforcement layer, such as fiber-reinforced plastic (FRP), in which reinforcing fibers are impregnated with a plastic base material. Carbon fibers are generally used as the reinforcing fibers.

[0005] DE 30 49 015 A1 shows a jacket for a high-pressure tank having a joint formed by joining open ends of two jacket components made of plastic material, the jacket for the high-pressure tank having flange elements projecting outwards in the diametrical direction near the joint, a joint strength of the joint being greater than or equal to a tensile strength of the plastic material.

[0006] DE 201 02 209 U1 shows a fuel tank whose casing consists of two thermoplastic parts that can be attached to each other via flanges. The flange attachment has a higher tensile strength than the plastic material of the casing. Summary of the invention

[0007] A high-pressure tank is filled with a predetermined gas, such as hydrogen, at high pressure. Therefore, its joints must have sufficient strength to prevent breakage due to the internal gas pressure.

[0008] A main object of the present invention is to provide a shell for a high pressure tank in which the joint thereof exhibits superior joint strength.

[0009] Another object of the present invention is to provide a jacket for a high pressure tank with sufficient reliability.

[0010] Yet another object of the present invention is to provide a method for manufacturing a jacket for a high-pressure tank to obtain the jacket for the high-pressure tank described above.

[0011] According to claim 1, a method for producing a shell for a high-pressure tank is provided to obtain the shell for the high-pressure tank by joining two shell components made of plastic material, the shell components being elements each including a flange element provided near an open end and including a bottom portion projecting outwardly in a diametrical direction and a side portion bent from the bottom portion to one side of a closed end, wherein an annular recess is defined by the bottom portion and the side portion, wherein the method for manufacturing a shell for the high-pressure tank comprises: a contact step of arranging end surfaces of the open ends of the two shell members in contact with each other; a joining step for joining the end faces of the open ends to each other by welding, thereby obtaining a joint; and a cutting step for cutting the bottom portions and the side portions of the flange members such that parts of the bottom portions remain, wherein the flange elements remain with a protrusion amount whereby a joint strength of the joint becomes greater than or equal to a tensile strength of the plastic material.

[0012] The high-pressure tank may have a joint formed by joining open ends of two shell members made of plastic material, the shell for the high-pressure tank further comprising flange members protruding outward in the diametrical direction near the joint, a joint strength of the joint being greater than or equal to a tensile strength of the plastic material, and a protrusion amount (residual protrusion amount) of the remaining flange members thus satisfying the following conditional expression (1). The wall thickness of the joint portion is obtained as the sum total of a wall thickness of the shell members and the remaining protrusion amount. Wall thickness of the connection ≥ (tensile strength of the plastic material / breaking stress of the connection) × wall thickness of the sheath components

[0013] In the above manner, the wall thickness of the joint is increased by allowing the flange elements to remain. Therefore, the joint area becomes large, and by this amount, the joint strength can be made greater than or equal to the tensile strength of the plastic material. This feature implies that when high-pressure gas is filled in the shell, the joint can be prevented from breaking first.

[0014] In particular, the above-described process can achieve a joint exhibiting superior joint strength. Therefore, the reliability of the shell for the high-pressure tank, and by extension, the reliability of the high-pressure tank in which such a shell is used, is made sufficient.

[0015] Furthermore, vibration welding, infrared heat welding, or hot plate welding are preferred as the welding method. This is because in this case, it is easy to insert and press tools into the annular recesses and generate or apply heat, making the joining process simple and easy to perform.

[0016] If the residual protrusion amount of the flange elements is too large, when the reinforcing layer is formed on the shell, the fiber material contained in the reinforcing layer may be subjected to tension by the flange elements, and therefore, there is a concern that localized stresses may be applied thereto. To overcome such concerns, it is preferable to set the residual protrusion amount to be less than or equal to a height difference allowable during winding when the reinforcing layer is formed.

[0017] Furthermore, if the corners are angled sections, there is a concern that the fiber material may be damaged if it catches on the corners and is stretched. Therefore, it is preferable to form rounded sections (R sections) or fillet sections (C sections) at the corner portions of the remaining flange elements. In this case, the fiber material is prevented from catching on the corners and thus prevents the fiber material from being damaged.

[0018] The joint strength of the connection is greater than or equal to the cohesive failure strength of the connection.

[0019] According to the present invention, the flange members are provided near the open ends of the shell members made of plastic material, so that after the joint is formed and the shell is maintained, parts of the flange members remain. For this reason, as the wall thickness of the joint becomes thicker and the joint area increases, the joint strength of the joint becomes greater than or equal to the tensile strength of the plastic material, or greater than or equal to the cohesive failure strength of the joint. In particular, superior joint strength is exhibited at the joint. Therefore, it is possible to provide a shell for the high-pressure tank that exhibits sufficient reliability and, further, a high-pressure tank using such a shell. Brief description of the drawings Fig. 1 is a schematic overall plan view of a shell for a high-pressure tank according to an embodiment of the present invention; Fig. 2 is a schematic overall plan view of a jacket component which is a part of the Fig. 1 shows the jacket for the high-pressure tank; Fig. 3 is an enlarged cross-sectional view of essential components, showing the vicinity of a Fig. 2 is enlarged; Fig. 4 is an enlarged cross-sectional view of essential components showing a state in which vibration welding tools are inserted into annular recesses formed in flange members; Fig. 5 is an enlarged cross-sectional view of essential components showing a state in which end surfaces of open ends of sheath members are brought into contact with each other; Fig. 6 is an enlarged cross-sectional view of essential components in continuation of Fig. 5, and shows a state in which the vicinity of the open ends is slightly compressed; Fig. 7 is an enlarged cross-sectional view of essential components showing a state in which the vibration welding tools are removed from the annular recesses together with the attainment of a joint; Fig. 8 is an enlarged cross-sectional view of essential components showing a state in which the flange members are cut away so that parts of their bottom portions remain; and Fig. 9 is an enlarged cross-sectional view of essential components showing a state in which a positional shift is generated between the end faces of the open ends of the sheath members. Description of versions

[0020] Hereinafter, preferred embodiments of a jacket for a high-pressure tank according to the present invention with respect to a method for producing the same will be shown and described in detail with reference to the accompanying drawings.

[0021] Fig. 1 is a schematic overall plan view of a shell for a high-pressure tank (hereinafter referred to simply as a "shell") 10 according to a present embodiment. The shell 10 is constructed by joining a first shell component 12 to a second shell component 14. According to the present embodiment, the first shell component 12 and the second shell component 14 have substantially the same shape as each other.

[0022] First, a description will be given with respect to the first sheath component 12 and the second sheath component 14. Fig. Figure 2 is a schematic overall plan view of the first shell component 12 before bonding. The first shell component 12 is a semi-cylindrical body with a hollow interior, one end of which is an open end 16 and the other end of which is a closed end 18 that is closed in a gradually converging manner. Near the open end 16, a flange element 20 is formed to protrude outward in the diametrical direction.

[0023] Fig. 3 is an enlarged cross-sectional view of essential components, in which the vicinity of a flange member 20 is enlarged. In addition, T1 in Fig. 3 a wall thickness of a side wall of the first casing component 12 (main body).

[0024] The flange member 20 is annular at a position slightly offset from the end face of the open end 16 toward the closed end 18 side. Furthermore, the flange member 20 includes a bottom portion 22 extending along the diametrical direction and a side portion 24 bent away from the bottom portion 22 to face the closed end 18 side. An annular recess 26 is defined by the bottom portion 22 and the side portion 24. Specifically, the annular recess 26 is a space formed between the main body side wall of the first shell member 12 and the side portion 24 of the flange member 20.

[0025] If the first shell component 12 and the second shell component 14 are joined together by vibration welding, a width W1 and a depth D1 of its annular recesses 26 can be set such that vibration welding tools 30 (see Fig. 4) can be inserted therein. Furthermore, a thickness T2 of the bottom portions 22 can be set to such an extent that the flange members 20 are not damaged during vibration welding. An initial protrusion amount L1 of the flange member 20 (the distance from the outer surface of the main body side wall of the first shell member 12 to the outer surface of the side portion 24 of the flange member 20) can be set, for example, to 1 to 3 times, and typically about 1.5 times, the wall thickness T1 of the first shell member 12.

[0026] On the inner surfaces of the side portion 24 facing the annular recess 26, a slope 32 is formed which is inclined at a predetermined angle θ in a direction away from the annular recess 26. This slope 32 serves to facilitate the detachment of the vibration welding tools 30 (see Fig. 4) and is also called the so-called extension angle.

[0027] Furthermore, as in Fig. 2, cutouts 34 are formed in the side portion 24 by cutting out portions of the side portion 24. For example, an anti-rotation tool is engaged with the cutouts 34.

[0028] A recess 40, which is recessed toward the side of the open end 16, is formed on an upper surface of the closed end 18. A projection 42 is provided at the bottom portion of the recess 40 and projects to one side away from the open end 16.

[0029] As previously noted, the second shroud member 14 is configured to conform to the first shroud member 12. Accordingly, the same components as those of the first shroud member 12 are designated by the same reference numerals, and a detailed description of these features is omitted.

[0030] Now, a description will be given regarding a method of production according to the present invention for obtaining the Fig. 1, comprising the first sheath component 12 and the second sheath component 14, which are configured in the manner described above.

[0031] The first shell member 12 and the second shell member 14 are manufactured, for example, by injection molding using a molten plastic material in an injection molding apparatus (not shown). Suitable examples of the plastic material include high-density polyethylene (HDPE) resin, which is a thermoplastic resin with hydrogen barrier properties. Furthermore, it should be understood that the boss members 42 and the flange members 20 are integrally molded with the main bodies. The slopes 32 and the cutouts 34 are also formed simultaneously with the molding.

[0032] If the first shell component 12 and the second shell component 14 have the same shape, these two components can be manufactured using the same mold. Therefore, since it is not necessary to prepare multiple molds, the mold cost can be reduced.

[0033] The first shell member 12 and the second shell member 14 obtained in the above manner are arranged opposite each other such that the end faces of the open ends 16 are separated from each other by a predetermined distance. If vibration welding is performed, then, as shown in Fig. 4, vibration welding tools 30 are inserted into the annular recesses 36. If necessary, an anti-rotation tool (not shown) is engaged with the cutouts 34 formed in the side portions 24 of the flange elements 20. This is preferred because it prevents rotation of the first shell component 12 and the second shell component 14 and facilitates subsequent processing steps.

[0034] Then, the vibration welding tools 30 are preloaded to press the respective flange members 20 of the first shell member 12 and the second shell member 14 in the directions of the arrows X, and the first shell member 12 and the second shell member 14 are brought close to each other. Then, as shown in Fig. 5, the end surfaces of the open ends 16 are brought into contact with each other (supported against each other). In other words, a contact step is performed and a contact point is formed.

[0035] Then a connection step is performed. In particular, as indicated by the arrow Y in Fig. 5, one of the vibration welding tools 30 within the annular recesses 26, for example, those on the upper side, vibrates along a diametrical direction of the first shell component 12. Consequently, frictional heat is generated at the contact point, and as a result, the contact point becomes soft or melts. Since the vibration welding tools 30 in the annular recesses 26 press the first shell component 12 and the second shell component 14 in directions to bring them closer to each other, as shown in Fig. As shown in Figure 6, these two elements 12 and 14 are pressed tightly together. Accompanying this compression, the plastic material that has softened or melted leaks out from the inner peripheral wall side or the outer peripheral wall side.

[0036] It should be noted that the vibration welding tool 30 on the bottom side may also be vibrated along a diametrical direction of the second shell member 12. Furthermore, such an action may also be performed assuming that it is possible to vibrate or rotate the vibration welding tools 30 in the circumferential direction of the first shell member 12 and the second shell member 14.

[0037] The vibration is stopped after a predetermined period of time has elapsed. Further, after a required period of time for pressing has elapsed, the vibration welding dies 30 are raised or lowered along the vertical direction and are separated from the annular recesses 26. At this time, since the slopes 32 are formed on the side portions 24, the vibration welding dies 30 can be easily separated from the annular recesses 26. Then, the plasticized or molten plastic material is cooled and solidified. Specifically, joining is performed at the contact point, and a joint 46 is obtained.

[0038] Then, a cutting step is performed. In this case, according to the conventional technique, the flange elements 20 are cut away from a base end, and grinding or polishing is performed so that the location where the flange elements 20 are provided is aligned with the main body side wall. In other words, the flange elements 20 are not left.

[0039] In contrast, according to the present embodiment, the cutting step is carried out for cutting along a cutting line CL such that portions of the flange elements 20 remain. In this case, the position of the cutting line CL (the amount by which the flange elements 20 are cut), or in other words, the Fig. 7 is set so that the joining strength of the joint 46 is greater than or equal to the tensile strength of the plastic material. The tensile strength of the plastic material can be obtained from a tensile test according to the Japanese Industrial Standard (JIS) using a test piece formed from a single member that does not have the joint 46 therein.

[0040] To ensure that the joint strength of the joint 46 is greater than the tensile strength of the plastic material, the tensile test is performed using a test piece cut out to include the joint 46 therein, and the remaining protrusion amount L2 of the flange members 20 can be determined based on the load (breaking stress) at the time of breakage. Furthermore, the tensile strength and the breaking stress may be average values ​​obtained by performing the test multiple times, or may be calculated values ​​obtained by subtracting values ​​of four times the standard deviation from the average values.

[0041] In particular, when a total sum of the residual projection amount L2 of the flange members 20 and the wall thickness T1 of the main body side wall is defined as the wall thickness of the joint 46, the values ​​of the tensile strength and the fracture stress can be set to values ​​satisfying the following expression (1). Wall thickness of the connection 46≥(tensile strength of the plastic material / rupture stress of the connection 46)×T1

[0042] For example, if a value calculated by calculating the right side of expression (1) is 3.4 mm, the minimum remaining protrusion amount L2 of the flange members 20 becomes (3.4 - T1) mm. Specifically, it suffices if the bottom portions 22 of the flange members 20 are cut away with a suitable cutting tool so that the flange members 20 protrude by (3.4 - T1) mm from the outer peripheral wall of the main body side wall. Moreover, the remaining protrusion amount L2 is preferably less than or equal to a height difference allowable during winding when the reinforcing layer is formed.

[0043] Along with the cutting described above, the side sections 24 and the majority of the bottom sections 22 are cut away in order to thereby remove the Fig. 8, whereby the state shown in Fig. 1 shown jacket 10. In this case, as in Fig.9 is exaggerated if the end surfaces are slightly shifted in position from each other, for example, a residual protrusion amount L2" of the second shell member 14 is smaller than that of the first shell member 12 by an amount of positional displacement. In particular, if the amount of positional displacement is indicated by Δd, a residual protrusion amount L2' of the first shell member 12 is a value obtained by subtracting Δd from the residual protrusion amount L2" of the second shell member 14. In this case, a total sum of the wall thickness T1 of the first shell member 12 and the residual protrusion amount L2' becomes the wall thickness of the joint 46.

[0044] It is preferable to create fillets at the corner portions of the remaining flange members 20 (bottom portions 22), thereby forming the rounded portions (R-portions) 50. In other words, it is preferable to bend the corner portions of the remaining bottom portions 20.

[0045] Furthermore, a reinforcing layer is provided which covers the jacket 10, and valves are attached to the insert elements 42, thereby producing the high-pressure tank. When the remaining protrusion amount L2 of the flange elements 20 is less than or equal to the height difference here, the stresses acting on the fiber material (carbon fibers or the like) contained in the reinforcing layer from the flange elements 20 are less than or equal to an allowable range. Furthermore, there are concerns that if the corners of the flange elements 20 are angled sections, the fiber material (carbon fibers or the like) could catch at the corners and thereby be locally stretched, and damage to the fiber material could occur. However, if the rounded sections (R-sections) 50 are formed in the manner described above, such concerns can be overcome.

[0046] In this high-pressure tank, the joint strength of the joint 46 of the shell 110 is greater than or equal to the tensile strength of the resin material constituting the base material of the first shell member 12 and the second shell member 14. Accordingly, when the high-pressure gas is filled into the shell 10, the joint 46 is prevented from breaking first. Finally, since portions other than the joint 46 of the shell 10 are made of a resin material with sufficient pressure resistance with respect to the filling pressure, the joint 46 also exhibits sufficient pressure resistance with respect to the filling pressure. In other words, a high-pressure tank exhibiting sufficient reliability can be obtained.

[0047] In contrast to the above-mentioned features, it is also considered that there may be cases where it is difficult to make the residual protrusion amount L2 of the flange members 20 large, such as when it is desired to make the height difference as small as possible during fiber winding. In this case, the residual protrusion amount L2 of the flange members 20 may be set such that the joint strength of the joint 46 is greater than or equal to a cohesive failure strength of the joint 46. Since the joint 46 is prevented from breaking first when the high-pressure gas is filled into the shell 10, a high-pressure tank exhibiting sufficient reliability can be realized.

[0048] The present invention is not particularly limited to the embodiments described above, and various modifications can be made thereto within a range that does not deviate from the spirit and scope of the present invention.

[0049] For example, instead of the rounded sections (R-sections), 50 throat sections (C-sections) can be formed.

[0050] Furthermore, the first sheath component 12 and the second sheath component 14 can be formed in different shapes from each other.

[0051] Furthermore, infrared heat welding can be performed instead of vibration welding, or vibration welding and infrared heat welding can be used in combination. When performing infrared heat welding, tools for performing infrared welding can be inserted into the annular recesses 26. Alternatively, hot plate welding can be performed. [Explanation of reference numbers] 10 Jacket for high-pressure tank 12, 14 Sheath components 16 open ends 18 closed ends 20 flange elements 22 floor sections 24 page sections 26 ring-shaped recesses 30 vibration welding tools 32 slopes 34 excerpts 46 Connection 50 rounded sections (R-sections)

Claims

[1] Method for producing a jacket (10) for a high-pressure tank for obtaining the jacket (10) for the high-pressure tank by joining two jacket components (12, 14) made of plastic material, wherein the shell components (12, 14) are elements each including a flange element (20) provided near an open end (16) and including a bottom portion (22) projecting outwardly in a diametrical direction and a side portion (24) bent from the bottom portion (22) to one side of a closed end (18), an annular recess (26) being defined by the bottom portion (22) and the side portion (24), wherein the method for producing a jacket (10) for the high-pressure tank comprises: a contact step of arranging end surfaces of the open ends (16) of the two sheath members (12, 14) in contact with each other; a joining step for joining the end faces of the open ends (16) together by welding, and thereby obtaining a joint (46); and a cutting step for cutting the floor sections (22) and the side sections (24) of the flange elements (20) such that parts of the bottom sections (22) remain, wherein the flange elements (20) remain with a projection amount (L2), whereby a connection strength of the connection (46) becomes greater than or equal to a tensile strength of the plastic material. [2] The method for manufacturing the shell (10) for the high-pressure tank according to claim 1, wherein, when a total sum of a wall thickness (T1) of the shell components (12, 14) and a projection amount (L2) of the remaining flange elements (20) is defined as the wall thickness of the joint (46), the projection amount (L2) of the remaining flange elements (20) is set such that the wall thickness of the joint (46) satisfies the following conditional expression (1): Wall thickness of the connection (46) ≥ (tensile strength of the plastic material / breaking stress of the connection (46)) × wall thickness (T1) of the sheath components (12, 14). [3] The method of manufacturing the shell (10) for the high pressure tank according to claim 1 or 2, wherein the welding is performed by vibration welding, infrared heat welding or hot plate welding. [4] The method of manufacturing the shell (10) for the high-pressure tank according to any one of claims 1 to 3, wherein the flange members (20) are left with a protrusion amount (L2) less than or equal to an allowable height difference during winding when a reinforcing layer is formed. [5] The method for manufacturing the shell (10) for the high-pressure tank according to any one of claims 1 to 4, wherein an R-section (50) or a C-section is formed at corner portions of the remaining flange members (20). [6] The method for manufacturing the shell (10) for the high-pressure tank according to one of claims 1 to 5, wherein the shell components (12, 14) are elements in which slopes (32) inclined in the direction away from the annular recesses (26) are formed on inner surfaces of the side portions (24) facing the annular recesses (26). [7] The method for manufacturing the shell (10) for the high-pressure tank according to any one of claims 1 to 6, wherein the shell components (12, 14) are elements in which cutouts (34) are formed in the side portions (24) by cutting out parts of the side portions (24).

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