Patent Publication Number: US-2023150211-A1

Title: High-pressure tank, method for manufacturing high-pressure tank, and method for manufacturing fiber-reinforced resin layer for high-pressure tank

Description:
INCORPORATION BY REFERENCE 
     This is a divisional application of U.S. patent application Ser. No. 17/094,122, filed Nov. 10, 2020, which claims the disclosure of Japanese Patent Application No. 2019-235219 filed on Dec. 25, 2019, both of which including the specification, drawings and abstract are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a high-pressure tank including a liner configured to store gas and a fiber-reinforced resin layer made of a fiber-reinforced resin and covering the outer surface of the liner, a method for manufacturing a high-pressure tank, and a method for manufacturing a fiber-reinforced resin layer for a high-pressure tank. 
     2. Description of Related Art 
     A tank including a tank body and a boss attached to an opening end in the longitudinal direction of the tank body is conventionally known as a high-pressure tank that is used to store and supply hydrogen etc. For example, the tank body includes a liner for holding hydrogen gas airtight and a fiber-reinforced resin layer formed by winding a fiber bundle of a fiber-reinforced resin around the outer surface of the liner to reinforce the liner. 
     In a known method for manufacturing a high-pressure tank, a fiber-reinforced resin layer is formed by winding a fiber bundle around the outer surface of a liner by, e.g., filament winding (hereinafter also simply referred to as the “FW process”) and curing the fiber bundle (e.g., Japanese Unexamined Patent Application Publication No. 2012-149739 (JP 2012-149739 A). 
     JP 2012-149739 A discloses a high-pressure tank including a liner and a fiber-reinforced plastic layer (fiber-reinforced resin layer) covering the outer surface of the liner. The fiber-reinforced plastic layer is composed of hoop layers formed by hoop-winding a resin-impregnated fiber bundle around the liner and helical layers formed by helically winding a resin-impregnated fiber bundle around the entire liner. The fiber-reinforced plastic layer is composed of a cylindrical cylinder section formed by the hoop layers and the helical layers and a pair of dome sections provided at both ends of the cylinder section and formed by the helical layers. 
     SUMMARY 
     In such a high-pressure tank as described in JP  2012 - 149739  A, the hoop layers provide the strength of the cylinder section, and the helical layers provide the strength of the dome sections. That is, the helical layers are also formed in the cylinder section but hardly contribute to the strength of the cylinder section. However, in the case where the fiber bundle is helically wound around the liner so as to run back and forth between both ends of the liner, the fiber bundle necessarily passes along the cylinder section. When the amount of fiber bundle required to provide sufficient strength of the dome sections is helically wound, the helical layers are also formed on the cylinder section. This unnecessarily increases the usage of the fiber-reinforced resin. 
     The disclosure provides a method for manufacturing a high-pressure tank that can reduce the usage of a fiber-reinforced resin. 
     A first aspect of the disclosure relates to a method for manufacturing a high-pressure tank including a liner configured to store gas and a fiber-reinforced resin layer made of a fiber-reinforced resin and covering an outer surface of the liner, the fiber-reinforced resin layer having a first reinforcing layer covering the outer surface of the liner and a second reinforcing layer covering an outer surface of the first reinforcing layer. The method includes: forming a cylinder member made of the fiber-reinforced resin and having fibers oriented in a circumferential direction of the cylinder member; forming two dome members made of the fiber-reinforced resin; forming a reinforcing body that is the first reinforcing layer by joining both end portions of the cylinder member and end portions of the two dome members; and forming on an outer surface of the reinforcing body the second reinforcing layer made of the fiber-reinforced resin and having fibers oriented across the two dome members. 
     According to the method of the disclosure, the cylinder member is formed. 
     The cylinder member is made of the fiber-reinforced resin and has fibers oriented in the circumferential direction of the cylinder member. Since the fibers in the cylinder member are oriented in the circumferential direction, the strength of the fiber-reinforced resin layer against hoop stress that is generated by a gas pressure is provided by an appropriate amount of fiber-reinforced resin. The two dome members made of the fiber-reinforced resin are also formed. Since the dome members are formed separately from the cylinder member using an appropriate amount of fiber-reinforced resin, the usage of the fiber-reinforced resin for the cylinder member is not increased due to formation of the dome members. 
     The second reinforcing layer made of the fiber-reinforced resin and having fibers oriented across the two dome members are formed on the outer surface of the reinforcing body. The fibers in the second reinforcing layer prevent the dome members from being separated from the cylinder member. The dome members are thus prevented from coming off from the end portions of the cylinder member by the gas pressure. The amount of fibers in the second reinforcing layer need only be large enough to prevent the dome members from coming off from the cylinder member. Accordingly, the usage of the fiber-reinforced resin is reduced as compared to the helical layers in the cylinder section of the conventional high-pressure tank. 
     As described above, according to the method of the disclosure, each part of the fiber-reinforced resin layer is formed using an appropriate amount of fiber-reinforced resin. Accordingly, the fiber-reinforced resin is not unnecessarily used, and the usage of the fiber-reinforced resin for the second reinforcing layer on the cylinder member is reduced as compared to the conventional high-pressure tank. 
     In the above method, the cylinder member may be formed by connecting a plurality of cylinder bodies each made of the fiber-reinforced resin and having fibers oriented in a circumferential direction of the cylinder body. With this configuration, even a long cylinder member can be easily formed. 
     In the above method, either or both of the two dome members may be formed so as to have a through hole, and the liner may be formed such that the liner covers an inner surface of the reinforcing body by introducing a resin material into the reinforcing body through the through hole. With this configuration, the liner can be easily formed inside the reinforcing body even after the reinforcing body is formed. Moreover, no mold for molding the liner is necessary unlike the case where the liner is formed by injection molding using resin. The liner covering the inner surface of the reinforcing body may be formed either after or before the second reinforcing layer is formed on the outer surface of the reinforcing body. 
     In this case, the liner may be formed by introducing the resin material that has fluidity into the reinforcing body, rotating the reinforcing body to cause the resin material to cover the inner surface of the reinforcing body, and solidifying the resin material covering the inner surface of the reinforcing body. With this configuration, as the reinforcing body is rotated, the inner surface of the reinforcing body moves upward with the resin material having fluidity thereon, and a part of the resin material flows down the inner surface of the reinforcing body due to its own weight. The resin material thus covers the inner surface of the reinforcing body. Accordingly, the liner covering the inner surface of the reinforcing body can be easily formed. 
     In the above method, the second reinforcing layer may be formed by: placing a plurality of resin-impregnated fiber bundles in such a manner that the fiber bundles extend in an axial direction of the reinforcing body at predetermined intervals in a circumferential direction of the reinforcing body and at a predetermined distance from the outer surface of the reinforcing body; and rotating portions on a first end side of the fiber bundles relative to portions on a second end side of the fiber bundles in the circumferential direction of the reinforcing body. The portions on the first end side of the fiber bundles are rotated relative to the portions on the second end side of the fiber bundles in the circumferential direction of the reinforcing body. Accordingly, the fiber bundles are tilted with respect to an axial direction of the cylinder member, and the gaps between the fiber bundles are eliminated and the fiber bundles partially overlap each other. The fiber bundles gradually approach the outer surface of the reinforcing body and are placed onto the outer surface of the reinforcing body with no gap between the fiber bundles. At this time, the fiber bundles tilted with respect to the axial direction are brought into close contact with an outer surface of the cylinder member. The portions on the first end side of the fiber bundles and the portions on the second end side of the fiber bundles are then twisted outside the end portions of the cylinder member and wound around the outer surfaces of the dome members. The second reinforcing layer covering the outer surface of the reinforcing body is formed in this manner. According to this method, the second reinforcing layer is formed on the outer surface of the reinforcing body without rotating the reinforcing body in the circumferential direction. It is therefore not necessary to provide a structure for rotating the reinforcing body (typically, a boss to which a rotating shaft is attached) on the opposite end of the high-pressure tank from the through hole. The axial direction and the circumferential direction of the reinforcing body are the same as the axial direction and the circumferential direction of the cylinder member, respectively. 
     In this case, at least one first tilted layer and at least one second tilted layer may be formed when forming the second reinforcing layer, the at least one first tilted layer being formed by rotating the portions on the first end side of the fiber bundles in a first direction, and the at least one second tilted layer being formed by rotating the portions on the first end side of the fiber bundles in a second direction that is opposite to the first direction. The first tilted layer is formed with the fiber bundles being tilted with respect to the axial direction and subjected to predetermined tension. Accordingly, when an expansive force is applied to the second reinforcing layer by the gas pressure, the first tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles with respect to the axial direction is eliminated. As a result, the reinforcing body is distorted. Similarly, the second tilted layer is formed with the fiber bundles being tilted in the opposite direction to the fiber bundles of the first tilted layer and subjected to predetermined tension. Accordingly, when the expansive force is applied to the second reinforcing layer by the gas pressure, the second tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles in the opposite direction to the tilt of the fiber bundles of the first tilted layer is eliminated. As a result, the reinforcing body is distorted. The fiber bundles of the first tilted layer and the fiber bundles of the second tilted layer are tilted in opposite directions. Accordingly, when the expansive force is applied to the second reinforcing layer by the gas pressure, the force in such a direction that the tilt of the fiber bundles of the first tilted layer is eliminated and the force in such a direction that the tilt of the fiber bundles of the second tilted layer is eliminated act to cancel each other out. This reduces distortion of the fiber-reinforced resin layer and therefore restrains reduction in strength of the high-pressure tank. 
     In the case where the at least one tilted layer and the at least one second tilted layer are formed, the number of the at least one first tilted layer and the number of the at least one second tilted layer may be the same. With this configuration, the force in such a direction that the tilt of the fiber bundles of the first tilted layer is eliminated and the force in such a direction that the tilt of the fiber bundles of the second tilted layer is eliminated effectively act to cancel each other out. This effectively reduces distortion of the fiber-reinforced resin layer due to the tilt of the fiber bundles and therefore effectively restrains reduction in strength of the high-pressure tank. 
     In the above method, after thermally curing the cylinder member, the cylinder member may be inserted into either or both of the two dome members, and the cylinder member and the either or both of the two dome members may be joined together. The strength of the cylinder member is thus increased in advance by the thermal curing. Accordingly, when fitting the cylinder member and the dome member together, the end portion of the dome member conforms to the end portion of the cylinder member, and the end portion of the cylinder member functions as a guide portion. The cylinder member and the dome member can thus be easily fitted together. In the case where the dome members are not thermally cured in advance, the dome member may be deformed when fitting the cylinder member and the dome member together. However, even when such deformation of the dome member occurs, the dome member can be pressed from the outside so that the dome member conforms to the cylinder member. The outer shape of the dome member can thus be adjusted or the dome member can be brought into close contact with the cylinder member. 
     In the above method, after thermally curing either or both of the two dome members, the either or both of the two dome members may be inserted into the cylinder member, and the either or both of the two dome members and the cylinder member may be joined together. The strength of the either or both of the two dome members is thus increased in advance by the thermal curing. Accordingly, when fitting the dome member and the cylinder member together, the end portion of the cylinder member conforms to the end portion of the dome member, and the end portion of the dome member functions as a guide portion. The dome member and the cylinder member can thus be easily fitted together. In the case where the cylinder member is not thermally cured in advance, the cylinder member may be deformed when fitting the dome member and the cylinder member together. However, even when such deformation of the cylinder member occurs, the cylinder member can be pressed from the outside so that the cylinder member conforms to the dome member. The outer shape of the cylinder member can thus be adjusted or the cylinder member can be brought into close contact with the dome member. 
     In the above method, the two dome members may be formed by winding a resin-impregnated fiber bundle around a predetermined die in such a manner that the fiber bundle covers an outer surface of the predetermined die and then dividing a resultant winding body of the fiber bundle wound around the predetermined die into parts. With this configuration, the fiber bundle can be easily wound on the predetermined die using, e.g., the FW process, and the two dome members can be easily formed by dividing the winding body of the fiber bundle into parts and removing the parts from the predetermined die. 
     A second aspect of the disclosure relates to a high-pressure tank including: a liner configured to store gas; and a fiber-reinforced resin layer made of a fiber-reinforced resin and covering an outer surface of the liner, the fiber-reinforced resin layer having a first reinforcing layer covering the outer surface of the liner and a second reinforcing layer covering an outer surface of the first reinforcing layer. The first reinforcing layer includes a cylinder member made of the fiber-reinforced resin and having fibers oriented in a circumferential direction of the cylinder member and two dome members made of the fiber-reinforced resin. Both end portions of the cylinder member are joined to end portions of the two dome members. The second reinforcing layer has fibers oriented across the two dome members. 
     According to the high-pressure tank of the disclosure, the first reinforcing layer includes the cylinder member made of the fiber-reinforced resin and having fibers oriented in the circumferential direction of the cylinder member. Since the fibers in the cylinder member are oriented in the circumferential direction, the strength of the fiber-reinforced resin layer against hoop stress that is generated by a gas pressure is provided by an appropriate amount of fiber-reinforced resin. Since the two dome members are formed separately from the cylinder member using an appropriate amount of fiber-reinforced resin, the usage of the fiber-reinforced resin for the cylinder member is not increased due to formation of the dome members. 
     The second reinforcing layer is made of the fiber-reinforced resin and has fibers oriented across the two dome members. The fibers in the second reinforcing layer prevent the dome members from being separated from the cylinder member. The dome members are thus prevented from coming off from the end portions of the cylinder member by the gas pressure. The amount of fibers in the second reinforcing layer need only be large enough to prevent the dome members from coming off from the cylinder member. Accordingly, the usage of the fiber-reinforced resin is reduced as compared to the helical layers in the cylinder section of the conventional high-pressure tank. 
     As described above, according to the high-pressure tank of the disclosure, each part of the fiber-reinforced resin layer is formed using an appropriate amount of fiber-reinforced resin. Accordingly, the fiber-reinforced resin is not unnecessarily used, and the usage of the fiber-reinforced resin for the second reinforcing layer on the cylinder member is reduced as compared to the conventional high-pressure tank. 
     In the above high-pressure tank, the second reinforcing layer may have, along an entire circumference of the second reinforcing layer, a plurality of fiber bundles oriented across the two dome members, the fiber bundles may include a first tilted layer in which the fiber bundles are tilted with respect to an axial direction of the first reinforcing layer and a second tilted layer in which the fiber bundles are tilted in an opposite direction to that of the fiber bundles of the first tilted layer with respect to the axial direction, and the second reinforcing layer may have the first and second tilted layers stacked on each other. The first tilted layer is formed with the fiber bundles being tilted with respect to the axial direction and subjected to predetermined tension. Accordingly, when an expansive force is applied to the second reinforcing layer by the gas pressure, the first tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles with respect to the axial direction is eliminated. As a result, the first reinforcing layer is distorted. Similarly, the second tilted layer is formed with the fiber bundles being tilted in the opposite direction to the fiber bundles of the first tilted layer and subjected to predetermined tension. Accordingly, when the expansive force is applied to the second reinforcing layer by the gas pressure, the second tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles in the opposite direction to the tilt of the fiber bundles of the first tilted layer is eliminated. As a result, the first reinforcing layer is distorted. The fiber bundles of the first tilted layer and the fiber bundles of the second tilted layer are tilted in opposite directions. Accordingly, when the expansive force is applied to the second reinforcing layer by the gas pressure, the force in such a direction that the tilt of the fiber bundles of the first tilted layer is eliminated and the force in such a direction that the tilt of the fiber bundles of the second tilted layer is eliminated act to cancel each other out. This reduces distortion of the fiber-reinforced resin layer and therefore restrains reduction in strength of the high-pressure tank. 
     A third aspect of the disclosure relates to a method for manufacturing a fiber-reinforced resin layer for a high-pressure tank including (i) a liner configured to store gas and (ii) the fiber-reinforced resin layer made of a fiber-reinforced resin and covering an outer surface of the liner, the fiber-reinforced resin layer having a first reinforcing layer covering the outer surface of the liner and a second reinforcing layer covering an outer surface of the first reinforcing layer. This method includes: forming a cylinder member made of the fiber-reinforced resin and having fibers oriented in a circumferential direction of the cylinder member; forming two dome members made of the fiber-reinforced resin; forming a reinforcing body that is the first reinforcing layer by joining both end portions of the cylinder member and end portions of the two dome members; and forming on an outer surface of the reinforcing body the second reinforcing layer made of the fiber-reinforced resin and having fibers oriented across the two dome members. 
     The disclosure thus provides a high-pressure tank, a method for manufacturing a high-pressure tank, and a method for manufacturing a fiber-reinforced resin layer for a high-pressure tank which can reduce the usage of a fiber-reinforced resin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    is a sectional view illustrating the structure of a high-pressure tank that is manufactured by a method according to an embodiment of the disclosure; 
         FIG.  2    is a partial sectional view illustrating the structure of a high-pressure tank that is manufactured by the method according to the embodiment of the disclosure; 
         FIG.  3    is a flowchart of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  4    is a partial sectional view illustrating a dome member forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  5    is a sectional view illustrating a dome member forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  6    is a perspective view illustrating a cylinder member forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  7    is a perspective view illustrating the cylinder member forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure, showing a part of an end portion in the axial direction of a cylinder member; 
         FIG.  8    is a perspective view illustrating a joining step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  9    is a sectional view illustrating the joining step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  10    is a perspective view illustrating a second reinforcing layer forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  11    is a perspective view illustrating the second reinforcing layer forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  12    is a sectional view illustrating a method for manufacturing a high-pressure tank according to a first modification of the disclosure; 
         FIG.  13    is a perspective view illustrating a method for manufacturing a high-pressure tank according to a second modification of the disclosure; 
         FIG.  14    is a sectional view illustrating a liner forming step of the method for manufacturing a high-pressure tank according to the embodiment of the disclosure; 
         FIG.  15    is a perspective view illustrating a method for manufacturing a high-pressure tank according to a third modification of the disclosure; 
         FIG.  16    is a perspective view illustrating a method for manufacturing a high-pressure tank according to a fourth modification of the disclosure; 
         FIG.  17    is a perspective view illustrating a method for manufacturing a high-pressure tank according to a fifth modification of the disclosure; 
         FIG.  18    is a sectional view illustrating a method for manufacturing a high-pressure tank according to a sixth modification of the disclosure; and 
         FIG.  19    is a sectional view illustrating a method for manufacturing a high-pressure tank according to a seventh modification of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Before describing a method for manufacturing a high-pressure tank  10  according to an embodiment of the disclosure, the configuration of the high-pressure tank  10  will be briefly described with reference to the drawings. Although the high-pressure tank  10  is herein described as a tank that is mounted on a fuel cell vehicle and that is filled with high-pressure hydrogen gas, the high-pressure tank  10  can also be used in other applications. The gas that can be used to fill the high-pressure tank  10  is not limited to high-pressure hydrogen gas. 
     As shown in  FIGS.  1  and  2   , the high-pressure tank  10  is a generally cylindrical high-pressure gas storage container with both ends rounded in a dome shape. The high-pressure tank  10  includes a liner  11  having gas barrier properties and a fiber-reinforced resin layer  12  made of a fiber-reinforced resin and covering the outer surface of the liner  11 . The fiber-reinforced resin layer  12  has a reinforcing body  20  and a second reinforcing layer  13 . The reinforcing body  20  is a first reinforcing layer and covers the outer surface of the liner  11 , and the second reinforcing layer  13  covers the outer surface of the reinforcing body  20 . The high-pressure tank  10  has an opening in its one end and has a boss  14  attached around the opening. The high-pressure tank  10  has no opening in the other end and has no boss attached to the other end. 
     The liner  11  extends along the inner surface of the reinforcing body  20 . The liner  11  is a resin member forming a housing space  17  that is filled with high-pressure hydrogen gas. The resin for the liner  11  is preferably a resin capable of holding filling gas (in this example, hydrogen gas) in the housing space  17 , namely a resin having satisfactory gas barrier properties. Examples of such a resin include thermoplastic resins such as polyamide, polyethylene, ethylene-vinyl alcohol copolymer resin (EVOH), and polyester and thermosetting resins such as epoxy resin. Instead of hydrogen gas, the liner  11  may be filled with other fuel gases. Examples of such fuel gases include compressed gases such as compressed natural gas (CNG) and various liquefied gases such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG). 
     The boss  14  is formed by machining a metal material such as aluminum or aluminum alloy into a predetermined shape. A valve  15  that controls the flow of hydrogen gas into and out of the housing space  17  is attached to the boss  14 . The valve  15  is provided with a seal member  15   a . The seal member  15   a  contacts the inner surface of the liner  11  in a protruding portion  22   a  of a dome member  22  described later and seals the housing space  17  of the high-pressure tank  10 . 
     The reinforcing body  20  covers the outer surface of the liner  11  and has a function to reinforce the liner  11  to improve mechanical strength, such as rigidity and pressure resistance, of the high-pressure tank  10 . As will be described later, the reinforcing body  20  has a cylindrical cylinder member  21  and two dome members  22 ,  23  connected to both end portions of the cylinder member  21 . The reinforcing body  20  is a member formed by joining the cylinder member  21  and the dome members  22 ,  23 . 
     The reinforcing body  20  is made of resin and fibers (continuous fibers). In the cylinder member  21 , the fibers extend along the entire circumference of the cylinder member  21  at an angle substantially perpendicular to the axial direction X of the cylinder member  21 . In other words, the fibers in the cylinder member  21  are oriented in the circumferential direction. The fibers are wound at least once around the liner  11 . Since the fibers in the cylinder member  21  are oriented in the circumferential direction of the cylinder member  21 , the strength of the fiber-reinforced resin layer  12  against hoop stress that is generated by an internal pressure (gas pressure) is provided by an appropriate amount of fiber-reinforced resin. In the dome members  22 ,  23 , on the other hand, the fibers are not oriented in the circumferential direction of the cylinder member  21  but the fibers extending in various directions crossing the circumferential direction are placed on top of one another. The strength of the fiber-reinforced resin layer  12  against stress that is generated by the internal pressure (gas pressure) is therefore provided by an appropriate amount of fiber-reinforced resin in the dome members  22 ,  23 . 
     In the present embodiment, the fibers in the cylinder member  21  are not continuous with (not connected to) the fibers in the dome members  22 ,  23 . As will be described later, the cylinder member  21  and the two dome members  22 ,  23  are formed separately, and the two dome members  22 ,  23  are then attached to both end portions of the cylinder member  21 . 
     The second reinforcing layer  13  covers the outer surface of the reinforcing body  20 . The second reinforcing layer  13  covers the entire dome members  22 ,  23 . The second reinforcing layer  13  is made of resin and fibers (continuous fibers). The fibers in the second reinforcing layer  13  are oriented parallel to, or obliquely at  45  degrees or less with respect to, the axial direction X of the cylinder member  21  and extend over the cylinder member  21  and across the two dome members  22 ,  23  located at both ends of the cylinder member  21 . These fibers prevent the dome members  22 ,  23  from moving outward in the axial direction X and thus prevent the dome members  22 ,  23  from coming off from the cylinder member  21  outward in the axial direction X by the gas pressure. 
     Next, a method for manufacturing the high-pressure tank  10  according to the embodiment of the disclosure will be described.  FIG.  3    is a flowchart illustrating the method for manufacturing the high-pressure tank  10 . As shown in  FIG.  3   , the method for manufacturing the high-pressure tank  10  includes a dome member forming step S 1 , a cylinder member forming step S 2 , a joining step S 3 , a second reinforcing layer forming step S 4 , and a liner forming step S 5 . Since the dome member forming step S 1  and the cylinder member forming step S 2  are independent of each other, the steps S 1 , S 2  may be performed either in parallel or sequentially in either order. 
     In the dome member forming step S 1 , as shown in  FIG.  4   , a resin-impregnated fiber bundle F is wound around the outer surface of a mandrel (predetermined die)  100  by, e.g., filament winding (FW process). Specifically, the mandrel  100  has a main body  101  and a shaft portion  102  extending outward from one end of the main body  101 . The main body  101  has a circular shape as viewed in the axial direction of the shaft portion  102 . The main body  101  has a groove  101   a  in the middle in the axial direction. The groove  101   a  is formed in the outer peripheral surface of the main body  101  and extends along the entire circumference of the main body  101 . The shaft portion  102  is rotatably supported by a rotation mechanism (not shown). 
     The mandrel  100  is rotated to wind the fiber bundle F such that the fiber bundle F covers the outer surface of the mandrel  100 . At this time, the fiber bundle F is also wound around the outer surface of the shaft portion  102  to form the cylindrical protruding portion  22   a  with a through hole  22   b  (see  FIG.  5   ). The fiber bundle F is wound at, e.g.,  40  degrees with respect to the axial direction of the shaft portion  102 . The material of the mandrel  100  is not particularly limited, but is preferably metal in order for the mandrel  100  to be strong enough not to deform when the fiber bundle F is wound around the mandrel  100 . 
     The resin with which the fiber bundle F is impregnated is not particularly limited, but is, e.g., a thermosetting resin. Preferred examples of the thermosetting resin include a phenol resin, a melamine resin, a urea resin, and an epoxy resin, and an epoxy resin is particularly preferable in terms of mechanical strength etc. Epoxy resins are typically resins produced by mixing a prepolymer such as a copolymer of bisphenol A and epichlorohydrin and a curing agent such as a polyamine and thermally curing the mixture. Epoxy resins have fluidity, namely epoxy resins are fluid when uncured and form a strong crosslinked structure when thermally cured. The resin with which the fiber bundle F is impregnated may be a thermoplastic resin. Examples of the thermoplastic resin include polyether ether ketone, polyphenylene sulfide, polyacrylic acid ester, polyimide, and polyamide. 
     Examples of fibers of the fiber bundle F include glass fibers, aramid fibers, boron fibers, and carbon fibers. Carbon fibers are particularly preferable in terms of lightweightness, mechanical strength, etc. 
     Next, the resultant winding body (fiber bundle F) formed on the outer surface of the mandrel  100  is divided into two parts using a cutter  110  (see  FIG.  4   ). As shown in  FIG.  5   , the two parts were then removed from the mandrel  100 . The two dome members  22 ,  23  are formed in this manner. 
     Specifically, in the state shown in  FIG.  4   , the boss  14  is attached to the outer surface of the protruding portion  22   a . The resin in the winding body (fiber bundle F) is then solidified, and a blade of the cutter  110  is inserted into the groove  101   a  of the mandrel  100  while rotating the mandrel  100 . The winding body is thus divided into two parts, and the two parts are then removed from the mandrel  100 . The two dome members  22 ,  23  are formed in this manner. The cutter  110  is not particularly limited, but may be, e.g., a rotating disk with a blade along its outer peripheral surface, a thin plate with a blade along its side surface, or a cutter that cuts the fiber bundle F using a laser beam. 
     Solidifying the resin in the fiber bundle F reduces deformation of the fiber bundle F when cutting with the cutter  110  and reduces deformation of the two dome members  22 ,  23  when removing from the mandrel  100 . 
     The process of solidifying the resin in the fiber bundle F is not particularly limited. However, for example, when the resin in the fiber bundle F (that is, the resin in the two dome members  22 ,  23 ) is a thermosetting resin, the resin may be precured. Precuring conditions (temperature and time), which vary depending on the type of resin in the fiber bundle F, are set so that the viscosity of the precured resin in the fiber bundle F is higher than that of the resin in the fiber bundle F when the fiber bundle F is wound on the mandrel  100  (viscosity before precuring). In this example, the resin in the fiber bundle F is precured until the resin in the fiber bundle F is no longer fluid. 
     The viscosity of the resin in the fiber bundle F when cutting with the cutter  110  and when removing from the mandrel  100  is preferably 0.05 to 100 Pa·s. With the viscosity being 0.05 Pa·s or higher, the deformation of the fiber bundle F when cutting with the cutter  110  and when removing from the mandrel  100  is sufficiently reduced. Moreover, with the viscosity being 100 Pa·s or lower, a large part of the resin in the fiber bundle F remains uncured. The presence of this uncured part restrains reduction in adhesive strength between the cylinder member  21  and the two dome members  22 ,  23  when curing the cylinder member  21  and the two dome members  22 ,  23  in a later step. Moreover, since the heating time of the resin is reduced, the manufacturing time of the dome members  22 ,  23  is reduced. The precuring conditions include heating for  10  to  120  minutes at temperatures higher than the gelation temperature of the resin with which the fiber bundle F is impregnated. For example, in the case where the fiber bundle F is impregnated with an epoxy resin, the precuring conditions may be 100 to 170° C. and 10 to 120 minutes. 
     The higher the viscosity of the resin in the fiber bundle F is, the more the deformation of the fiber bundle F when cutting with the cutter  110  is reduced and the more the deformation of the dome members  22 ,  23  when removing from the mandrel  100  is reduced. The resin in the fiber bundle F may be cured completely (e.g., until physical properties such as Young&#39;s modulus become stable) (complete curing). In this case, however, the manufacturing time of the dome members  22 ,  23  is increased. It is therefore desirable to stop heating and allow to cool when the resin in the fiber bundle F reaches such a viscosity that the two parts can be easily removed from the mandrel  100  (e.g., 0.05 Pa·s) or higher. 
     “Thermal curing” in the specification and the claims represents a concept including precuring and complete curing. 
     When the resin in the fiber bundle F is a thermoplastic resin, the resin in the fiber bundle F may be solidified by cooling the fiber bundle F when the resin has fluidity, i.e., the resin is fluid. In this case as well, the deformation of the fiber bundle F when cutting with the cutter  110  is reduced, and the deformation of the fiber bundle F when removing the two dome members  22 ,  23  from the mandrel  100  is also reduced. 
     In the example described above, the fiber bundle F is cut with the cutter  110  after solidifying the resin in the fiber bundle F. However, the fiber bundle F may be cut with the cutter  110  without solidifying the resin in the fiber bundle F. In this case, the resin in the fiber bundle F may be solidified after cutting the fiber bundle F with the cutter  110 . 
     It is not essential to solidify the resin in the fiber bundle F. However, in the case where the resin in the fiber bundle F is not solidified, the resin is sticky, and it is difficult to remove the fiber bundle F from the mandrel  100  (the fiber bundle F tends to be deformed). It is therefore preferable to, e.g., apply a release agent to the surface of the mandrel  100  before winding the fiber bundle F around the mandrel  100  or remove the two dome members  22 ,  23  from the mandrel  100  at a reduced speed in order to reduce the deformation of the fiber bundle F. 
     In the example described above, the boss  14  is attached to the outer surface of the protruding portion  22   a  after winding the fiber bundle F around the outer surface of the mandrel  100 . However, a boss may be attached in advance to the joint portion between the main body  101  and the shaft portion  102  of the mandrel  100 , and the fiber bundle F may be wound around the outer surface of the mandrel  100  with the boss attached to the joint portion. In this case, a part of the boss is covered with and held by the fiber bundle F. The boss can thus be firmly fixed by the fiber bundle F. 
     In the cylinder member forming step S 2 , as shown in  FIG.  6   , the cylinder member  21  is formed by what is called centrifugal winding (CW process), namely by attaching a fiber sheet F 2  to the inner surface of a rotating cylindrical die  200 . Specifically, the cylindrical die  200  is rotated at a predetermined rotational speed by a rotation mechanism (not shown). The material of the cylindrical die  200  is not particularly limited, but is preferably metal in order for the cylindrical die  200  to be strong enough not to deform when the fiber sheet F 2  is attached to the cylindrical die  200 . 
     A feed roller  210  of a feed device (not shown) that feeds the fiber sheet F 2  from a roll of the fiber sheet F 2  is disposed in the cylindrical die  200 . The fiber sheet F 2  is fed while rotating the cylindrical die  200 . The fiber sheet F 2  is thus attached to the inner surface of the cylindrical die  200 . The cylinder member  21  is formed in this manner. 
     The fiber sheet F 2  has at least fibers oriented in the circumferential direction of the feed roller  210 . The cylinder member  21  having fibers oriented in the circumferential direction can thus be obtained. 
     Examples of the fiber sheet F 2  include what is called a uni-direction (UD) sheet formed by interlacing a plurality of fiber bundles aligned in a single direction with restraining yarn, and a fiber sheet formed by interlacing a plurality of fiber bundles aligned in a single direction with a plurality of fiber bundles crossing these fiber bundles, e.g., oriented perpendicularly to these fiber bundles. 
     The fiber sheet F 2  may be a fiber sheet not pre-impregnated with resin or a fiber sheet pre-impregnated with resin. In the case where the fiber sheet F 2  is a fiber sheet not pre-impregnated with resin, the fiber sheet F 2  is fed to the inner surface of the rotating cylindrical die  200  by the feed roller  210 . With the fiber sheet F 2  thus attached to the inner surface of the cylindrical die  200  by centrifugal force and friction force, resin is poured into the cylindrical die  200  to impregnate the fiber sheet F 2  with the resin. Alternatively, resin may be poured into the cylindrical die  200  while feeding the fiber sheet F 2 . Specifically, the fiber sheet F 2  may be impregnated with resin while attaching the fiber sheet F 2  to the inner surface of the cylindrical die  200 . In the case where the fiber sheet F 2  is a fiber sheet not pre-impregnated with resin or in the case where the fiber sheet F 2  is a fiber sheet pre-impregnated with resin, air bubbles can be removed from the fiber sheet F 2  by centrifugal force by rotating the cylindrical die  200  with the fiber sheet F 2  being heated as necessary so that the resin has fluidity, i.e. the resin is fluid. This debubbling process is performed as necessary. 
     The resin with which the fiber sheet F 2  is impregnated is not particularly limited, but is, e.g., a thermosetting resin. Like the fiber bundle F, preferred examples of the thermosetting resin include a phenol resin, a melamine resin, a urea resin, and an epoxy resin, and an epoxy resin is particularly preferable in terms of mechanical strength etc. 
     Like the fiber bundle F, examples of the fibers of the fiber sheet F 2  include glass fibers, aramid fibers, boron fibers, and carbon fibers, and carbon fibers are particularly preferable in terms of lightweightness, mechanical strength, etc. 
     As shown in  FIG.  7   , the end portions in the axial direction X of the cylinder member  21  formed on the inner surface of the cylindrical die  200  become gradually thinner towards the edges in the axial direction X of the cylinder member  21 . As shown in  FIG.  2   , steps are therefore less likely to be formed at the joint portion between the outer surface of the cylinder member  21  and the outer surfaces of the two dome members  22 ,  23  when the cylinder member  21  is combined with the two dome members  22 ,  23 . This reduces formation of voids between the second reinforcing layer  13  and the reinforcing body  20  due to the steps at the joint portion between the cylinder member  21  and the two dome members  22 ,  23 . 
     In order to make both end portions in the axial direction X of the cylinder member  21  gradually thinner toward the edges in the axial direction X of the cylinder member  21 , the fiber bundles in the end portions in the axial direction X (lateral direction) of the fiber sheet F 2  are preferably interlaced such that the thickness of the fiber bundles becomes gradually smaller toward the edges in the axial direction X of the fiber sheet F 2 . Both end portions in the axial direction X of the cylinder member  21  may be made gradually thinner toward the edges in the axial direction X of the cylinder member  21  by pressing both end portions in the axial direction X of the cylinder member  21  by rollers etc. Even when a plurality of layers of the fiber sheet F 2  is formed on the inner surface of the cylindrical die  200 , the fiber bundles and the resin are pressed radially outward against the inner surface of the cylindrical die  200  due to the centrifugal force generated by rotation of the cylindrical die  200 , no gap in the thickness direction is left in the end portions of the layers of the fiber sheet F 2 . 
     Thereafter, the cylinder member  21  is removed from the cylindrical die  200 . At this time, the cylinder member  21  is solidified and then separated from the inner surface of the cylindrical die  200 . Solidifying the cylinder member  21  reduces deformation of the cylinder member  21  when removing from the cylindrical die  200 . 
     As in the case of the fiber bundle F in the dome member forming step S 1 , the process of solidifying the cylinder member  21  is not particularly limited. However, for example, when the resin of the cylinder member  21  (that is, the fiber sheet F 2 ) is a thermosetting resin, the resin may be precured. Precuring conditions (temperature and time), which vary depending on the type of resin of the cylinder member  21 , are set so that the viscosity of the precured resin of the cylinder member  21  is higher than that of the resin of the fiber sheet F 2  fed on the cylindrical die  200  (or the resin poured into the cylindrical die  200 ). In this example, the resin in the fiber sheet F 2  is precured until the resin in the fiber sheet F 2  is no longer fluid. It is preferable to precure the resin while rotating the cylindrical die  200 . Regardless of whether the fiber sheet F 2  is a fiber sheet pre-impregnated with resin or a fiber sheet not pre-impregnated with resin, air is present between the fiber sheet F 2  and the cylindrical die  200  or between the layers of the fiber sheet F 2  when the fiber sheet F 2  is formed on the inner surface of the cylindrical die  200 . By rotating the cylindrical die  200  when precuring the resin having a reduced viscosity due to heat, the air can be removed by the centrifugal force generated by the rotation of the cylindrical die  200 . This reduces formation of voids in the cylinder member  21 . 
     The viscosity of the resin of the cylinder member  21  when removing from the cylindrical die  200  is preferably 0.05 to 100 Pa·s. With the viscosity being 0.05 Pa·s or higher, the deformation of the cylinder member  21  when removing from the cylindrical die  200  is sufficiently reduced. With the viscosity being 100 Pa·s or lower, a large part of the resin of the cylinder member  21  remains uncured. The presence of this uncured part restrains reduction in adhesive strength between the cylinder member  21  and the two dome members  22 ,  23  when curing the cylinder member  21  and the two dome members  22 ,  23  in a later step. Moreover, since the heating time of the resin is reduced, the manufacturing time of the cylinder member  21  is reduced. The precuring conditions include heating for  10  to  120  minutes at temperatures higher than the gelation temperature of the resin with which the fiber sheet F 2  is impregnated. For example, in the case where the fiber sheet F 2  is impregnated with an epoxy resin, the precuring conditions may be 100 to 170° C. and 10 to 120 minutes. 
     The higher the viscosity of the resin of the cylinder member  21  is, the more the deformation of the cylinder member  21  when removing from the cylindrical die  200  is reduced. The resin of the cylinder member  21  may be cured completely (e.g., until physical properties such as Young&#39;s modulus become stable) (complete curing). In this case, however, the manufacturing time of the cylinder member  21  is increased. It is therefore desirable to stop heating and allow to cool when the resin of the cylinder member  21  reaches such a viscosity that the cylinder member  21  can be easily removed from the cylindrical die  200  (e.g., 0.05 Pa·s) or higher. 
     When the resin of the cylinder member  21  is a thermoplastic resin, the cylinder member  21  may be solidified by cooling the cylinder member  21  when the resin has fluidity, i.e., the resin is fluid. In this case as well, the deformation of the cylinder member  21  when removing from the cylindrical die  200  is reduced. 
     It is not essential to solidify the cylinder member  21 . However, in the case where the cylinder member  21  is not solidified, the cylinder member  21  is sticky and it is difficult to remove the cylinder member  21  from the cylindrical die  200  (the cylinder member  21  tends to be deformed). It is therefore preferable to, e.g., apply a release agent to the inner surface of the cylindrical die  200  before attaching the fiber sheet F 2  to the inner surface of the cylindrical die  200  or remove the cylinder member  21  from the cylindrical die  200  at a reduced speed in order to reduce the deformation of the cylinder member  21 . Alternatively, the cylindrical die  200  may be composed of a plurality of members that can be separated in the radial direction, and the cylindrical die  200  may be removed from the cylinder member  21  little by little (one member by one member). 
     In the example described above, the cylinder member  21  is formed on the inner surface of the cylindrical die  200 . However, the cylinder member  21  may be formed by other methods. For example, the cylinder member  21  may be formed by attaching the fiber sheet F 2  to the outer surface of a cylindrical die or by hoop-winding a resin-impregnated fiber bundle around the cylindrical die by the FW process. However, in the case where the cylinder member  21  is thermally cured (precured or completely cured) or cooled, the cylinder member  21  shrinks during curing or due to temperature decrease and it becomes difficult to remove the cylinder member  21  from the outer surface of the cylindrical die. It is therefore preferable to form the cylinder member  21  on the inner surface of the cylindrical die  200 . 
     As described above, in the cylinder member forming step S 2 , the cylinder member  21  made of a fiber-reinforced resin and having fibers oriented in the circumferential direction is formed using the cylindrical die  200 . Since the fibers in the cylinder member  21  are oriented in the circumferential direction, the strength of the fiber-reinforced resin layer  12  against the hoop stress that is generated by the gas pressure is provided by an appropriate amount of fiber-reinforced resin. In the dome member forming step  51 , the two dome members  22 ,  23  are formed using the mandrel  100 . The dome members  22 ,  23  are thus formed separately from the cylinder member  21  by using an appropriate amount of fiber-reinforced resin. The usage of the fiber-reinforced resin for the cylinder member  21  is therefore not increased due to formation of the dome members  22 ,  23 . 
     The dome members  22 ,  23  are formed using the mandrel  100 , and the cylinder member  21  is formed using the cylindrical die  200 . Accordingly, the cylinder member  21  and the dome members  22 ,  23  are formed without directly winding the fiber bundle etc. around the liner  11 . Since the liner  11  is not subjected to a tightening force due to hoop winding, helical winding, etc., it is not necessary to increase the strength of the liner  11  so that the liner  11  is not deformed by the tightening force. The thickness (wall thickness) of the liner  11  can therefore be reduced. Accordingly, the capacity of the liner  11  can be increased and the weight of the liner  11  can be reduced. 
     Reducing the thickness of the liner  11  also has the following effects. For example, when gas is continuously used at a pressure close to the lower limit gas pressure (the lower limit of the normal use range) of the high-pressure tank  10 , the liner  11  may thermally contract due to decreases in temperature and internal pressure caused by adiabatic expansion. However, by reducing the thickness of the liner  11 , the liner  11  more easily expands due to the internal pressure, and thermal contraction of the liner  11  is therefore reduced. Accordingly, the lower limit gas pressure can be set to a lower value, and a larger amount of gas can be discharged from the high-pressure tank  10 . 
     In the joining step S 3 , as shown in  FIGS.  8  and  9   , both end portions  21   a  of the cylinder member  21  and end portions  22   c ,  23   a  of the two dome members  22 ,  23  are joined to form the reinforcing body  20  that is the first reinforcing layer. 
     Specifically, the end portion  22   c  of the dome member  22  and the end portion  23   a  of the dome member  23  are fitted in the end portions  21   a  of the cylinder member  21 . Since the end portions  21   a  of the cylinder member  21 , the end portion  22   c  of the dome member  22 , and the end portion  23   a  of the dome member  23  have a cylindrical shape, the end portion  22   c  of the dome member  22  and the end portion  23   a  of the dome member  23  contact the end portions  21   a  of the cylinder member  21  along the entire circumference. An adhesive  300  (see  FIG.  9   ) may be applied between the cylinder member  21  and the dome members  22 ,  23 . This configuration further restrains the dome members  22 ,  23  from coming off from the cylinder member  21  in a later step. Moreover, since the adhesive  300  fills the gaps between the cylinder member  21  and the dome members  22 ,  23 , a resin material for the liner  11  is prevented from flowing into the gaps between the cylinder member  21  and the dome members  22 ,  23  in the liner forming step S 5 . The material of the adhesive  300  is not particularly limited, but is preferably, e.g., a thermosetting resin such as an epoxy resin. The adhesive  300  may be a resin having the same components as those of the cylinder member  21  or the dome members  22 ,  23 . Even when the adhesive  300  is not used, the resin contained in the second reinforcing layer  13  oozes from the second reinforcing layer  13  and fills the gaps between the cylinder member  21  and the dome members  22 ,  23  during curing in the second reinforcing layer forming step S 4 . The resin material for the liner  11  is therefore restrained from flowing into the gaps between the cylinder member  21  and the dome members  22 ,  23  in the liner forming step S 5 . 
     It is preferable that the dome members  22 ,  23  whose end portions  22   c ,  23   a  are to be located inside the end portions  21   a  of the cylinder member  21  when fitting the dome members  22 ,  23  and the cylinder member  21  together be thermally cured (precured or completely cured) in advance. The strength of the dome members  22 ,  23  is thus increased in advance by the thermal curing. Accordingly, when fitting the dome members  22 ,  23  and the cylinder member  21  together, the end portions  21   a  of the cylinder member  21  conform to the end portions  22   c ,  23   a  of the dome members  22 ,  23 , and the dome members  22 ,  23  function as guide portions. The cylinder member  21  and the dome members  22 ,  23  can thus be easily fitted together. In the case where the cylinder member  21  whose end portion  21   a  are to be located outside the end portions  22   c ,  23   a  of the dome members  22 ,  23  is not thermally cured in advance, the cylinder member  21  may be deformed when fitting the cylinder member  21  and the dome members  22 ,  23  together. However, even when such deformation of the cylinder member  21  occurs, the outer shape of the cylinder member  21  can be adjusted as shown in  FIG.  7    or the cylinder member  21  can be brought into close contact with the dome members  22 ,  23 , because the cylinder member  21  can be pressed from the outside. The boss  14  is attached to the dome member  22 , and the reinforcing body  20  and the second reinforcing layer  13  are supported by the boss  14  in a later step. It is therefore preferable that the dome member  22  have increased strength so that it can support the boss  14 , the reinforcing body  20 , and the second reinforcing layer  13 . Accordingly, it is effective to thermally cure the dome member  22  in advance. 
     In the second reinforcing layer forming step S 4 , the second reinforcing layer  13  made of a fiber-reinforced resin and having fibers placed across the two dome members  22 ,  23  is formed so as to cover the outer surface of the reinforcing body  20 . The fiber-reinforced resin layer  12  having the reinforcing body  20  and the second reinforcing layer  13  is formed in this manner. The second reinforcing layer  13  can be formed by, e.g., methods shown in  FIGS.  10  and  11   . Specifically, a support mechanism (not shown) is attached to the boss  14  mounted on the reinforcing body  20  so that the support mechanism holds the reinforcing body  20 .  FIGS.  10  and  11    illustrate the reinforcing body  20  placed horizontally. The reinforcing body  20  may be placed vertically in order to prevent the reinforcing body  20  from bending downward under gravity. 
     A plurality of resin-impregnated fiber bundles F 4  is then placed over the reinforcing body  20  such that the fiber bundles F 4  extend in the axial direction X of the reinforcing body  20  at predetermined angular intervals in the circumferential direction of the reinforcing body  20  and at a predetermined distance from the outer surface of the reinforcing body  20 . At this time, the fiber bundles F 4  are fed through feed parts  400  of a feed device, and the distal ends of the fiber bundles F 4  are held by holding members  410 . 
     The resin with which the fiber bundles F 4  are impregnated is not particularly limited, but is, e.g., a thermosetting resin. Like the fiber bundle F, preferred examples of the thermosetting resin include a phenol resin, a melamine resin, a urea resin, and an epoxy resin, and an epoxy resin is particularly preferable in terms of mechanical strength etc. 
     Like the fiber bundle F, examples of fibers of the fiber bundles F 4  include glass fibers, aramid fibers, boron fibers, and carbon fibers, and carbon fibers are particularly preferable in terms of lightweightness, mechanical strength, etc. 
     Thereafter, in the state shown in  FIG.  10   , the feed parts  400  and the holding members  410  are rotated in opposite directions in the circumferential direction of the reinforcing body  20 . The portions on a first end side (feed part  400  side) of the fiber bundles F 4  and the portions on a second end side (holding member  410  side) of the fiber bundles F 4  are thus rotated relative to each other in the circumferential direction of the reinforcing body  20 . In this example, the portions on the first end side of the fiber bundles F 4  are rotated in a first direction, and the portions on the second end side of the fiber bundles F 4  are rotated in a second direction opposite to the first direction. As shown in  FIG.  11   , the fiber bundles F 4  are thus tilted with respect to the axial direction X of the cylinder member  21 , and the gaps between the fiber bundles F 4  are eliminated and the fiber bundles F 4  partially overlap each other. The fiber bundles F 4  gradually approach the outer surface of the reinforcing body  20  and are placed onto the outer surface of the reinforcing body  20  with no gap between the fiber bundles F 4 . At this time, the fiber bundles F 4  tilted with respect to the axial direction X are brought into close contact with the outer surface of the cylinder member  21 , and movement of those portions of the fiber bundles F 4  which are in close contact with the outer surface of the cylinder member  21  is restricted due to the adhesive force of the resin. The portions on the first end side of the fiber bundles F 4  and the portions on the second end side of the fiber bundles F 4  are then twisted by the feed parts  400  and the holding members  410  outside the end portions of the cylinder member  21  and thus wound around the outer surfaces of the dome members  22 ,  23 . In this manner, the second reinforcing layer  13  is formed so as to cover the outer surface of the reinforcing body  20 . Thereafter, unnecessary portions of the fiber bundles F 4  are cut away. The first layer of the fiber bundles F 4  is thus formed. 
     The fiber bundles F 4  are provided in order to prevent the dome members  22 ,  23  from coming off from the cylinder member  21  outward in the axial direction X by the gas pressure. The fiber bundles F 4  are therefore placed in the axial direction X of the cylinder member  21 . The tilt angle of the fiber bundles F 4  (the angle of the fiber bundles F 4  with respect to the axial direction X of the cylinder member  21 ) is not particularly limited, but the fiber bundles F 4  are oriented preferably at an angle larger than  0  degrees and equal to or smaller than  45  degrees, more preferably at an angle larger than  0  degrees and equal to or smaller than  20  degrees, with respect to the axial direction X of the cylinder member  21 . 
     Thereafter, the second layer of the fiber bundles F 4  is formed by a method similar to that for the first layer. When forming the second layer, the portions on the first end side (feed part  400  side) of the fiber bundles F 4  are rotated in the second direction, and the portions on the second end side (the holding member  410  side) of the fiber bundles F 4  are rotated in the first direction. In the case where the third and subsequent layers of the fiber bundles F 4  are formed, odd-numbered layers (first tilted layers) are formed in a manner similar to that of the first layer, and even-numbered layers (second tilted layers) are formed in a manner similar to that of the second layer. 
     The number of layers of the fiber bundles F 4  is not particularly limited as long as the second reinforcing layer  13  has sufficient strength. However, the number of layers of the fiber bundles F 4  is preferably  2  to  12 , and more preferably  2 . The smaller the number of layers of the fiber bundles F 4  is, the more preferable, as long as the second reinforcing layer  13  has sufficient strength. It is preferable that the number of first tilted layers and the number of second tilted layers are the same. The first tilted layer is formed with the fiber bundles F 4  being tilted with respect to the axial direction X and subjected to predetermined tension, and is later cured with the fiber bundles F 4  in the tilted state. Accordingly, when an expansive force is applied to the second reinforcing layer  13  by the gas pressure, the first tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles F 4  with respect to the axial direction X is eliminated. As a result, the reinforcing body  20  is distorted. Similarly, the second tilted layer is formed with the fiber bundles F 4  being tilted in the opposite direction to the fiber bundles F 4  of the first tilted layer and subjected to predetermined tension, and is later cured with the fiber bundles F 4  in the tilted state. Accordingly, when the expansive force is applied to the second reinforcing layer  13  by the gas pressure, the second tilted layer is subjected to a force in such a direction that the tilt of its fiber bundles F 4  in the opposite direction to the tilt of the fiber bundles F 4  of the first tilted layer is eliminated. As a result, the reinforcing body  20  is distorted. The fiber bundles F 4  of the first tilted layer and the fiber bundles F 4  of the second tilted layer are tilted in opposite directions. Accordingly, when the expansive force is applied to the second reinforcing layer  13  by the gas pressure, the force in such a direction that the tilt of the fiber bundles F 4  of the first tilted layer is eliminated and the force in such a direction that the tilt of the fiber bundles F 4  of the second tilted layer is eliminated act to cancel each other out. This reduces distortion of the fiber-reinforced resin layer  12  and therefore reduces distortion of the high-pressure tank  10 . This configuration thus restrains reduction in strength of the high-pressure tank  10 . 
     In this example, the number of first tilted layers and the number of second tilted layers are the same. Accordingly, the force in such a direction that the tilt of the fiber bundles F 4  of the first tilted layer is eliminated and the force in such a direction that the tilt of the fiber bundles F 4  of the second tilted layer is eliminated effectively act to cancel each other out. This effectively reduces distortion of the fiber-reinforced resin layer  12  due to the tilt of the fiber bundles F 4  and therefore effectively restrains reduction in strength of the high-pressure tank  10 . The number of first tilted layers may be different from the number of second tilted layers. For example, only the first tilted layer(s) or only the second tilted layer(s) may be formed. 
     A predetermined number of layers of the fiber bundles F 4  is formed to form the second reinforcing layer  13 . Thereafter, the reinforcing body  20  and the second reinforcing layer  13  are heated and cured, e.g., at 100 to 170° C. for 10 to 120 minutes. At this time, the adhesive  300  permeates into the reinforcing body  20  and the second reinforcing layer  13 . 
     As described above, the second reinforcing layer  13  has fibers placed across the two dome members  22 ,  23 . The fibers of the second reinforcing layer  13  prevent the dome members  22 ,  23  from being separated from the cylinder member  21 . The dome members  22 ,  23  are thus restrained from coming off from both end portions of the cylinder member  21  by the gas pressure. The amount of fibers in the second reinforcing layer  13  need only be large enough to prevent the dome members  22 ,  23  from coming off from the cylinder member  21 . Accordingly, the usage of the fiber-reinforced resin is reduced as compared to the helical layers in the cylinder section of the conventional high-pressure tank. 
     According to the second reinforcing layer forming step S 4 , the second reinforcing layer  13  is formed on the outer surface of the reinforcing body  20  without rotating the reinforcing body  20  in the circumferential direction. It is therefore not necessary to provide a structure for rotating the reinforcing body  20  (typically, a boss to which a rotating shaft is attached) on the opposite end of the high-pressure tank  10  from the through hole  22   b.    
     In the example described above, as shown in  FIGS.  10  and  11   , the second reinforcing layer  13  is formed on the outer surface of the reinforcing body  20  by rotating the fiber bundles F 4  in the circumferential direction of the reinforcing body  20 . However, the second reinforcing layer  13  may be formed by other methods. For example, the second reinforcing layer  13  may be formed using what is called sheet winding, namely by winding a resin-impregnated fiber sheet around the outer surface of the reinforcing body  20 . In this case, fibers in the fiber sheet are preferably oriented in the axial direction X of the cylinder member  21 . However, like the fiber bundles F 4 , the fibers in the fiber sheet may be oriented at an angle larger than 0 degrees and equal to or smaller than 45 degrees with respect to the axial direction X of the cylinder member  21 , or may be oriented at an angle larger than 0 degrees and equal to or smaller than 20 degrees with respect to the axial direction X of the cylinder member  21 . In the case where the second reinforcing layer  13  is formed using the fiber bundles F 4  or the fiber sheet, the fibers may be oriented parallel to the axial direction X. The second reinforcing layer  13  may be formed on the outer surface of the reinforcing body  20  by the FW process. In the case where the FW process is used, it is preferable to cure the reinforcing body  20  before forming the second reinforcing layer  13  in order to prevent deformation of the reinforcing body  20 . 
     In the example described above, as shown in  FIG.  2   , one end of the second reinforcing layer  13  (the end on the boss  14  side, the first ends of the fiber bundles F 4 ) extends to a position immediately before the boss  14 . However, as in a first modification shown in  FIG.  12   , one end of the second reinforcing layer  13  may cover a part of the outer surface of the boss  14 . With this configuration, the boss  14  can be held by the second reinforcing layer  13 . The boss  14  is therefore reliably prevented from coming off from the reinforcing body  20 . 
     In the example described above, as shown in  FIG.  1   , the other end of the second reinforcing layer  13  (the opposite end from the boss  14 , the second ends of the fiber bundles F 4 ) has a smooth, generally spherical surface. However, as in a second modification shown in  FIG.  13   , the other end of the second reinforcing layer  13  may have a protrusion  13   b  with a recessed portion  13   a . With this configuration, the other end of the second reinforcing layer  13  can be held by, e.g., holding member  450  shown in  FIG.  13   . This improves workability in a later step and improves mountability of the high-pressure tank  10  on a fuel cell vehicle. The protrusion  13   b  with the recessed portion  13   a  can be easily formed by adjusting the cutting position when cutting the fiber bundles F 4  in the state shown in  FIG.  11   . 
     In the liner forming step S 5 , as shown in  FIG.  14   , a resin material M is introduced into the fiber-reinforced resin layer  12  through the through hole  22   b  in the protruding portion  22   a  of the reinforcing body  20 . The resin material M is then solidified while rotating the fiber-reinforced resin layer  12 . The liner  11  is formed in this manner. 
     Specifically, the internal space of the fiber-reinforced resin layer  12  communicates with the outside through the through hole  22   b . A nozzle  500  that discharges the resin material M is inserted through the through hole  22   b , and the resin material M is introduced into the internal space of the fiber-reinforced resin layer  12  through the nozzle  500 . The nozzle  500  is then removed from the through hole  22   b.    
     As described above, the resin material M is preferably a resin having satisfactory gas barrier properties. Examples of such a resin include thermoplastic resins such as polyamide, polyethylene, ethylene-vinyl alcohol copolymer resin (EVOH), and polyester and thermosetting resins such as epoxy resin, and polyamide is preferred. The resin material M may be a resin material that has fluidity at normal temperature or may be a powdery material. 
     The reinforcing body  20  is then rotated so that the resin material M covers the inner surface of the reinforcing body  20 . Specifically, the internal space of the fiber-reinforced resin layer  12  is heated to a predetermined temperature or higher as necessary. With the resin material M having fluidity of low viscosity (0 to 0.05 Pa·s), the fiber-reinforced resin layer  12  is rotated in the circumferential direction about its axis extending in the horizontal direction, while moving both ends of the fiber-reinforced resin layer  12  alternately up and down (see  FIG.  14   ). As the fiber-reinforced resin layer  12  is rotated, the inner surface of the fiber-reinforced resin layer  12  moves upward with the resin material M having fluidity thereon, and a part of the resin material M flows down the inner surface of the fiber-reinforced resin layer  12  due to its own weight. The resin material M is thus brought into contact with, and covers, the entire inner surface of the reinforcing body  20 . In the case where the resin material M is a thermosetting resin, the internal space of the fiber-reinforced resin layer  12  is heated to cure the resin material M. The liner  11  is thus formed. In the case where the resin material M is a thermoplastic resin, the internal space of the fiber-reinforced resin layer  12  is cooled to solidify the resin material M that is in contact with, and covers, the inner surface of the fiber-reinforced resin layer  12 . The liner  11  is thus formed. In this example, the liner  11  is formed by reaction injection molding using two or more kinds of liquid materials having low molecular weight and fluidity of low viscosity at normal temperature as the resin material M. In this case, the internal space of the fiber-reinforced resin layer  12  is heated to produce a polymer from a monomer. The internal space of the fiber-reinforced resin layer  12  is then cooled to solidify the polymer. The liner  11  is thus formed. 
     According to the liner forming step S 5 , the liner  11  can be easily formed inside the fiber-reinforced resin layer  12  even after the fiber-reinforced resin layer  12  is formed. Moreover, no mold for molding the liner is necessary unlike the case where the liner is formed by injection molding using resin. 
     The high-pressure tank  10  is completed by attaching the valve  15  to the boss  14 . 
     In the present embodiment, as described above, the cylinder member  21  made of the fiber-reinforced resin and having the fibers oriented in the circumferential direction is formed. Since the fibers in the cylinder member  21  are oriented in the circumferential direction, the strength of the fiber-reinforced resin layer  12  against hoop stress that is generated by the gas pressure is provided by an appropriate amount of fiber-reinforced resin. The dome members  22 ,  23  can be formed separately from the cylinder member  21  using an appropriate amount of fiber-reinforced resin. Accordingly, the usage of the fiber-reinforced resin for the cylinder member  21  is not increased due to formation of the dome members  22 ,  23 . 
     The second reinforcing layer  13  made of the fiber-reinforced resin and having the fibers oriented across the two dome members  22 ,  23  is formed on the outer surface of the reinforcing body  20 . The fibers in the second reinforcing layer  13  prevent the dome members  22 ,  23  from being separated from the cylinder member  21 . The dome members  22 ,  23  are thus prevented from coming off from the end portions of the cylinder member  21  by the gas pressure. The amount of fibers in the second reinforcing layer  13  need only be large enough to prevent the dome members  22 ,  23  from coming off from the cylinder member  21 . Accordingly, the usage of the fiber-reinforced resin is reduced as compared to the helical layers in the cylinder section of the conventional high-pressure tank. 
     As described above, according to the method for manufacturing the high-pressure tank  10  of the present embodiment, each part of the fiber-reinforced resin layer  12  is formed using an appropriate amount of fiber-reinforced resin. Accordingly, the fiber-reinforced resin is not unnecessarily used, and the usage of the fiber-reinforced resin for the second reinforcing layer  13  on the cylinder member  21  is reduced as compared to the conventional high-pressure tank. 
     The embodiment disclosed herein should be construed as illustrative in all respects, not restrictive. The scope of the disclosure is not limited to the above description of the embodiment. 
     For example, in the example described in the above embodiment, the two dome members  22 ,  23  are formed by filament winding in the dome member forming step S 1 . However, the disclosure is not limited to this. For example, as in a third modification of the disclosure shown in  FIG.  15   , the two dome members  22 ,  23  may be formed by tape placement, namely by pressing and applying the fiber bundle F to the surface of a dome-shaped die (predetermined die)  160  using a roller  150 . In this case, a plurality of dies (e.g., two dies) with different shapes can be used according to the shapes of the dome members  22 ,  23 . That is, the two dome members  22 ,  23  can be formed using at least one die (one or more dies). 
     In the example described in the above embodiment, the liner  11  is formed after the reinforcing body  20  and the second reinforcing layer  13  are formed. However, the disclosure is not limited to this. For example, as in a fourth modification of the disclosure shown in  FIG.  16   , when combining both end portions  21   a  of the cylinder member  21  and the end portions  22   c ,  23   a  of the two dome members  22 ,  23  in the joining step S 3 , the cylinder member  21  and the two dome members  22 ,  23  may be placed so as to cover a resin liner  611  formed in advance. In this case, the liner forming step S 5  is not performed. The liner  611  can be formed by a conventionally known manufacturing method. However, the strength of the liner  611  need not be increased because no fiber bundle is wound around the outer surface of the liner  611  by the FW process. Accordingly, the thickness of the liner  611  can be reduced as compared to the conventional liner. The liner  611  may be made of a metal material such as aluminum alloy instead of the resin material. 
     In this manufacturing method, the outside diameter of the liner  611  is made slightly smaller than the inside diameter of the cylinder member  21  so that the liner  611  can be easily inserted through the cylinder member  21 . Accordingly, with the liner  611  covered by the cylinder member  21  and the two dome members  22 ,  23 , there is clearance between the inner surface of the reinforcing body  20  and the outer surface of the liner  611 . However, with the high-pressure tank  10  (the liner  611 ) filled with hydrogen gas, the liner  611  expands due to the gas pressure, and the inner surface of the reinforcing body  20  is therefore kept in close contact with the outer surface of the liner  611 . 
     In the example described in the above embodiment, the cylinder member  21  is composed of a single member. However, the disclosure is not limited to this. For example, as in a fifth modification of the disclosure shown in  FIG.  17   , the cylinder member  21  may be formed by connecting two or more (three in  FIG.  17   ) cylinder bodies  121 . In this case, the two or more cylinder bodies  121  may first be joined to form the cylinder member  21 , and the dome members  22 ,  23  may then be joined to both end portions of the cylinder member  21 . Alternatively, the cylinder bodies  121  may first be joined to the dome members  22 ,  23 , one cylinder body  121  for each dome member  22 ,  23 , and the resultant members may then be joined together. The cylinder bodies  121  can be formed by a method similar to that for the cylinder member  21  described above. That is, the cylinder bodies  121  are made of a fiber-reinforced resin and has fibers oriented in the circumferential direction. As in the case where the cylinder member  21  and the dome members  22 ,  23  are joined together, the cylinder bodies  121  may be connected together with an end portion of one of the cylinder bodies  121  located inside an end portion of the other cylinder body  121 . Alternatively, the cylinder bodies  121  may be made to abut on each other and bonded together using an adhesive. For example, in the case where a plurality of types of cylinder bodies  121  with different lengths or sizes is formed, a plurality of dies with different lengths or sizes can be used according to the types of cylinder bodies  121 . That is, the cylinder member  21  can be formed using at least one die (one or more dies). 
     In the example described in the above embodiment, the end portions  21   a  of the cylinder member  21  and the end portions  22   c ,  23   a  of the dome members  22 ,  23  are fitted together in the joining step S 3 . However, the disclosure is not limited to this. The end portions  21   a  of the cylinder member  21  and the end portions  22   c ,  23   a  of the dome members  22 ,  23  may be made to abut on each other and bonded together using an adhesive. 
     As in a sixth modification of the disclosure shown in  FIG.  18   , the reinforcing body  20  may be composed of two members (e.g., the two dome members  22 ,  23 ). In this case, the high-pressure tank  10  can be manufactured by performing all the steps of the above embodiment except the cylinder member forming step S 2 , namely the dome member forming step S 1 , the joining step S 3 , the second reinforcing layer forming step S 4 , and the liner forming step S 5 , in a manner similar to that of the above embodiment. In the case where the two dome members  22 ,  23  are joined together, it is preferable to make the end portion  22   c  of the dome member  22  and the end portion  23   a  of the dome member  23  to abut on each other and bond them together using an adhesive, because the end portion  22   c  of the dome member  22  and the end portion  23   a  of the dome member  23  have the same size. 
     In the example described in the above embodiment, after thermally curing the dome members  22 ,  23 , the end portions  22   c ,  23   a  of the dome members  22 ,  23  are inserted into the end portions  21   a  of the cylinder member  21 , and the dome members  22 ,  23  and the cylinder member  21  are joined together. However, the disclosure is not limited to this. As in a seventh modification of the disclosure shown in  FIG.  19   , after thermally curing the cylinder member  21 , the end portions  21   a  of the cylinder member  21  may be inserted into the end portions  22   c ,  23   a  of the dome members  22 ,  23 , and the cylinder member  21  and the dome members  22 ,  23  may be joined together. In this case, the cylinder member  21  and the dome members  22 ,  23  can be easily fitted together. Moreover, the outer shape of the dome members  22 ,  23  can be adjusted, and the dome members  22 ,  23  can be in close contact with the cylinder member  21 . 
     In the example described in the above embodiment, the liner  11  is formed in the liner forming step S 5  by rotating the fiber-reinforced resin layer  12  so that the resin material having fluidity covers the entire inner surface of the fiber-reinforced resin layer  12 . However, the disclosure is not limited to this. For example, the liner  11  may be formed by blow molding or thermal spraying. In blow molding, the liner  11  is formed by extruding a thermoplastic resin material, softened by heating, in a tubular shape into the fiber-reinforced resin layer  12  through the through hole  22   b , introducing compressed air into the tubular resin material so that the resin material contacts and covers the inner surface of the fiber-reinforced resin layer  12 , and solidifying the resin material. In thermal spraying, the liner  11  is formed by spraying a liquid or softened resin material onto the inner surface of the fiber-reinforced resin layer  12 . 
     In the example described in the above embodiment, the liner  11  is formed after the second reinforcing layer  13  is formed on the outer surface of the reinforcing body  20 . However, the disclosure is not limited to this. The second reinforcing layer  13  may be formed on the outer surface of the reinforcing body  20  after the liner  11  is formed inside the reinforcing body  20 . In this case, it is preferable that the liner  11  be made of a thermosetting resin such as epoxy resin so that the liner  11  is not softened when curing the second reinforcing layer  13 . 
     In the example described in the above embodiment, the dome member  22  with the through hole  22   b  is formed in the dome member forming step S 1 . However, the disclosure is not limited to this. For example, the through hole  22   b  may be formed in the fiber-reinforced resin layer  12  after the joining step S 3 . 
     In the example described in the above embodiment, the cylinder member  21  is formed using a die. However, the disclosure is not limited to this. For example, the cylinder member  21  may be formed by winding a fiber sheet or a fiber bundle around a liner formed by a conventionally known manufacturing method, and two dome members  22 ,  23  may be joined to the cylinder member  21 . 
     In the example described in the above embodiment, the through hole  22   b  is provided only in the dome member  22 , and the boss  14  is attached to only one end of the high-pressure tank  10 . However, the disclosure is not limited to this. A through hole may be formed in both of the dome members  22 ,  23 , and a boss may be attached to both one end and the other end of the high-pressure tank  10 .