Patent Publication Number: US-11378231-B2

Title: Pressure vessel manufacturing method

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2018-228535 filed on Dec. 5, 2018 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a pressure vessel manufacturing method. 
     2. Description of Related Art 
     Japanese Patent Application Publication No. 2018-519480 (JP 2018-519480 A) discloses a method of forming a pressure vessel by connecting tubes having a resin liner to each other through a flexible connector and then folding the flexible connector. This flexible connector has a corrugated part. A dry braiding is put on the resin liner, and resin is further applied to the braiding. 
     SUMMARY 
     In the field of manufacturing of a pressure vessel of which the outer side of a resin cylindrical connecting part is reinforced with a reinforcing part as in JP 2018-519480 A, there is a known method in which a connecting part that connects vessel main bodies to each other is pleated and curved, and then heated and pressurized to manufacture a pressure vessel. Curving the connecting part in this method causes a difference in the length in a curving direction of the connecting part between the inner side and the outer side of the curve, which in turn causes a difference in the state of an inner surface of the connecting part between these sides. 
     More particularly, on the outer side of the curve, the length in the curving direction of the connecting part is long and the pleated part is stretched out in the curving direction, leaving a small clearance between ridges of the pleated part and the reinforcing part. Conversely, on the inner side of the curve, the length in the curving direction of the connecting part is short and the pleated part is less stretched out in the curving direction, so that a larger space is left between ridges of the pleated part and the reinforcing part than on the outer side of the curve. A large space between the ridges of the pleated part and the reinforcing part means a high degree of freedom for deformation of the pleated part. Thus, when the connecting part is curved and the inside of the curved connecting part is pressurized, the part of the liner on the inner side of the curve may become prone to deformation compared with the part thereof on the outer side of the curve. There is room for improvement here. 
     In view of this fact, the present disclosure aims to devise a pressure vessel manufacturing method that can ensure that when a pleated tubular body and a reinforcing part are curved and the inside of the curved tubular body is pressurized, a part of the tubular body on the inner side of the curve is less prone to deformation. 
     A pressure vessel manufacturing method of a first aspect of the present disclosure includes: molding a resin tubular body that connects one vessel main body and another vessel main body to each other, with a pleated part formed at least at part of the tubular body in an axial direction; forming a reinforcing part that reinforces the tubular body on the outer circumferential side of the tubular body; curving the tubular body and the reinforcing part such that an axis of the tubular body draws a curved line; and heating the tubular body and the reinforcing part while pressurizing the inside of the curved tubular body. In the molding the tubular body, the height of first pleats of the pleated part that are disposed on the inner side of the curve relative to the axis is set to be smaller than the height of second pleats of the pleated part that are disposed on the outer side of the curve relative to the axis. 
     In the pressure vessel manufacturing method of the first aspect, the height of the first pleats is set to be smaller than the height of the second pleats. This allows the first pleats to be stretched out along the curving direction at a part of the tubular body on the inner side of the curve when the tubular body and the reinforcing part are curved. In other words, the clearance between ridges of the first pleats and the reinforcing part is reduced. As a result, the area of contact between the first pleats and the reinforcing part is increased and the degree of freedom for deformation of the first pleats is reduced. Thus, this method can ensure that when a pleated tubular body and a reinforcing part are curved and then the inside of the curved tubular body is pressurized, the part of the tubular body on the inner side of the curve is less prone to deformation. 
     In a pressure vessel manufacturing method of a second aspect of the present disclosure, the amount of a pressure applied to pressurize the inside of the tubular body may be set such that the first pleats after heating form a curved part extending along the reinforcing part. 
     In the pressure vessel manufacturing method of the second aspect, a predetermined pressure is applied in the process of heating the tubular body while pressurizing the inside of the tubular body, so that not only the second pleats but also the first pleats are deformed so as to have a smaller height after heating. Moreover, the first pleats after heating form a curved part extending along the reinforcing part. Thus, applying the predetermined pressure to the first pleats and the second pleats can cause not only the second pleats but also the first pleats to assume a shape extending along the axial direction. As a result, the area of contact between the first pleats and the reinforcing part is increased compared with when a low pressure is applied, and the clearance between the first pleats and the reinforcing part after heating can be reduced accordingly. 
     The present disclosure can ensure that when a pleated tubular body and a reinforcing part are curved and then the inside of the curved tubular body is pressurized, the part of the tubular body on the inner side of the curve is less prone to deformation. 
    
    
     
       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 numerals denote like elements, and wherein: 
         FIG. 1  is a plan view of a pressure vessel unit having a high-pressure vessel according to a first embodiment; 
         FIG. 2A  is a side view of a liner in the high-pressure vessel of  FIG. 1 ; 
         FIG. 2B  is a vertical sectional view of the liner in the high-pressure vessel of  FIG. 1 , as seen from a direction orthogonal to an axial direction; 
         FIG. 3A  is a plan view of the liner in the high-pressure vessel of  FIG. 1 ; 
         FIG. 3B  is a horizontal sectional view of the liner in the high-pressure vessel of  FIG. 1 ; 
         FIG. 4  is a vertical sectional view of a connecting part in the high-pressure vessel of  FIG. 1 , as seen from the axial direction; 
         FIG. 5  is a partial vertical sectional view showing a close-up of part of the connecting part of  FIG. 2B ; 
         FIG. 6A  is a vertical sectional view showing how an unprocessed connecting part in the high-pressure vessel of  FIG. 1  is molded; 
         FIG. 6B  is a vertical sectional view showing the unprocessed connecting part of  FIG. 6A  in a curved state; 
         FIG. 6C  is an illustration showing how the unprocessed connecting part of  FIG. 6B  is heated and pressurized; 
         FIG. 6D  is a partial vertical sectional view showing the connecting part of  FIG. 1  upon completion; 
         FIG. 7  is a partial vertical sectional view showing part of the connecting part of  FIG. 6D ; 
         FIG. 8  is a partial vertical sectional view showing a connecting part of a high-pressure vessel according to a second embodiment upon completion; and 
         FIG. 9  is a partial vertical sectional view showing part of a connecting part of a high-pressure vessel according to a modified example. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A vehicle  10  to which a high-pressure vessel  30  as an example of a pressure vessel according to a first embodiment is applied, the high-pressure vessel  30 , and a manufacturing method of the high-pressure vessel  30  will be described. 
     Overall Configuration 
       FIG. 1  shows part of the vehicle  10 . The vehicle  10  includes a fuel cell stack  12 , a supply pipe  14 , a driving motor (not shown), and a pressure vessel unit  20 . The arrows FR, UP, and OUT shown in  FIG. 1  indicate a vehicle front side, a vehicle upper side, and an outer side in a vehicle width direction, respectively. 
     The fuel cell stack  12  and the pressure vessel unit  20  are connected to each other through the supply pipe  14 . The fuel cell stack  12  generates electricity through electrochemical reactions between a hydrogen gas G that is an example of a gas supplied from the pressure vessel unit  20  and compressed air that is supplied from an air compressor (not shown). Part of electricity resulting from electricity generation in the fuel cell stack  12  is supplied to the driving motor (not shown). The driving motor is driven by electricity supplied from the fuel cell stack  12 . Driving power of the driving motor is transmitted to rear wheels (not shown) of the vehicle  10 . 
     The pressure vessel unit  20  is disposed on a vehicle lower side of a floor panel (not shown) that forms a floor surface of a vehicle cabin of the vehicle  10 . The pressure vessel unit  20  includes a case  22 , a lead-out pipe  24 , and the high-pressure vessel  30  to be described later. The high-pressure vessel  30  and the lead-out pipe  24  are disposed inside the case  22 . The lead-out pipe  24  connects the high-pressure vessel  30  and the supply pipe  14  to each other. 
     Configuration of Main Parts 
     Next, the high-pressure vessel  30  will be described. 
     For example, the high-pressure vessel  30  has five vessel main bodies  32  and four connecting parts  34 . More particularly, the high-pressure vessel  30  has a structure in which the five vessel main bodies  32  and the four connecting parts  34  are connected in series to one another, with each connecting part  34  connecting two vessel main bodies  32  to each other. In the high-pressure vessel  30 , the four connecting parts  34  are curved (so as to be folded) alternately in opposite directions, so that the five vessel main bodies  32  are disposed in a row in the vehicle width direction inside the case  22 . 
     The high-pressure vessel  30  of this embodiment is formed, for example, by separately molding the vessel main bodies  32  and the connecting parts  34  and then integrating these vessel main bodies  32  and connecting parts  34  by adhesion. However, the vessel main bodies  32  and the connecting parts  34  may instead be integrally molded. Specifically, the high-pressure vessel  30  may be formed by integrally molding the five vessel main bodies  32  and the four connecting parts  34  in a straight line, and then curving the four connecting parts  34  so as to be folded. 
     Vessel Main Body 
     The vessel main body  32  has a substantially cylindrical shape elongated in a vehicle front-rear direction. Both end portions of the vessel main body  32  have a hemispherical shape. Moreover, the vessel main body  32  has, for example, a cross-sectional structure in which a fiber-reinforced part  52  (see  FIG. 4 ) is laid on an outer circumferential surface of a liner  36  (see  FIG. 4 ) to be described later. For example, the vessel main body  32  has the same layered structure as the connecting part  34  to be described later. The vessel main body  32  is formed, for example, by blow molding. 
     For example, the five vessel main bodies  32  are disposed with both front ends and rear ends thereof in the vehicle front-rear direction aligned in the vehicle width direction. Here, to make distinctions among the five vessel main bodies  32 , the vessel main body  32  farthest away from the lead-out pipe  24  will be referred to as a vessel main body  32 A, and the vessel main body  32  next to the vessel main body  32 A will be referred to as a vessel main body  32 B. Similarly, to make distinctions among the other three vessel main bodies  32 , these will be referred to as vessel main bodies  32 C,  32 D,  32 E toward the lead-out pipe  24 . When no distinctions are made among the five vessel main bodies  32 , these will be referred to as the vessel main bodies  32 . 
     The vessel main body  32 A is an example of one vessel main body. The vessel main body  32 A is closed at one end (rear end) in the vehicle front-rear direction. The vessel main body  32 A is open at the other end (front end). At the other end of the vessel main body  32 A, one end of the connecting part  34 , to be described later, is connected by adhesion. 
     The vessel main body  32 B is an example of another vessel main body. The vessel main body  32 B is open at both ends. At the other end (front end) of the vessel main body  32 B, the other end of the connecting part  34 , to be described later, is connected. In other words, the connecting part  34  connects the vessel main body  32 A and the vessel main body  32 B to each other. 
     The vessel main bodies  32 C,  32 D,  32 E have the same structure as the vessel main body  32 B. At the other end of the vessel main body  32 E in the vehicle front-rear direction, one end of the lead-out pipe  24  in the vehicle front-rear direction is connected. 
     Connecting Part 
     The connecting part  34  is formed as a cylindrical member, elongated in one direction, that is curved toward a direction orthogonal to that one direction (axial direction) so as to have a U-shape as a whole. The hydrogen gas G can flow through an inside of the connecting part  34 . One connecting part  34  is connected to the vessel main body  32 A and the vessel main body  32 B by adhesion. In other words, one connecting part  34  connects the vessel main body  32 A and the vessel main body  32 B to each other. The outside diameter of the connecting part  34  is smaller than the outside diameter of the vessel main body  32 . 
       FIG. 4  shows a cross-section of the connecting part  34  as seen from the axial direction. In the subsequent description, the axial direction of the connecting part  34  will be referred to as an X-direction, regardless of whether or not the connecting part  34  is curved. A direction which is orthogonal to the X-direction and in which, when the connecting part  34  is curved, a portion of the connecting part  34  on the inner side of the curve and a portion thereof on the outer side of the curve are located side by side will be referred to as a Y-direction (vertical direction). Moreover, a direction orthogonal to both the X-direction and the Y-direction will be referred to as a Z-direction (lateral direction). In addition, a radial direction relative to a center C of the connecting part  34  as seen from the X-direction will be referred to as an R-direction. 
     The connecting part  34  has the liner  36  as an example of a tubular body, and the fiber-reinforced part  52  as an example of a reinforcing part that reinforces the liner  36 . 
     Liner 
       FIG. 2A  shows the liner  36  before being curved, as seen from the Z-direction. For example, the liner  36  is made of a nylon resin having gas barrier properties. The liner  36  has one pleated part  38  formed at a center part in the X-direction, and two cylindrical parts  39  formed one on each side of the pleated part  38  in the X-direction. For example, the length in the X-direction of the pleated part  38  is about a quarter of the length in the X-direction of the liner  36 . 
       FIG. 2B  shows a vertical section of the liner  36  cut along an X-Y plane at a center in the Z-direction. In the subsequent description, an imaginary axis passing through the center C of the liner  36  (see  FIG. 4 ) and extending in the X-direction will be referred to as an axis K. In the Y-direction, the side corresponding to the outer side of the curve relative to the axis K will be referred to as an upper side, and the side corresponding to the inner side of the curve relative to the axis K will be referred to as a lower side. The lengths of the two cylindrical parts  39  in the X-direction are set to be equal. The two cylindrical parts  39  have no ridges and grooves formed therein. The two cylindrical parts  39  each have an outer circumferential surface  39 A. 
     A surface of the pleated part  38  at a portion having a maximum outside diameter will be referred to as an outer circumferential surface  38 A. The pleated part  38  has first pleats  42  and the second pleats  44  disposed respectively on the lower side and the upper side in the Y-direction as seen from the Z-direction. The first pleats  42  are a portion of the pleated part  38  that is disposed on the inner side of the curve relative to the axis K when the liner  36  is curved. The second pleats  44  are a portion of the pleated part  38  that is disposed on the outer side of the curve relative to the axis K when the liner  36  is curved. 
       FIG. 5  shows enlarged cross-sections of the first pleats  42  and the second pleats  44  as seen from the Z-direction. 
     The first pleats  42  have a plurality of ridges  42 A protruding from a center in the Y-direction of the first pleats  42  toward the fiber-reinforced part  52 , and a plurality of grooves  42 B depressed from the center in the Y-direction toward the axis K. The ridges  42 A and the grooves  42 B are alternately arrayed in the X-direction. The pitch in the X-direction of the ridges  42 A and the pitch in the X-direction of the grooves  42 B have an equal length. In the Y-direction, the length from a height position corresponding to a lower end of the groove  42 B to a height position corresponding to an upper end of the ridge  42 A will be defined as a height h 1  [mm] of the first pleats  42 . 
     The second pleats  44  have a plurality of ridges  44 A protruding from a center in the Y-direction of the second pleats  44  toward the fiber-reinforced part  52 , and a plurality of grooves  44 B depressed from the center in the Y-direction toward the axis K. The ridges  44 A and the grooves  44 B are alternately arrayed in the X-direction. The pitch in the X-direction of the ridges  44 A and the pitch in the X-direction of the grooves  44 B have an equal length, which is also equal to the pitch in the X-direction of the ridges  42 A and the pitch in the X-direction of the grooves  42 B. In the Y-direction, the length from a height position corresponding to a lower end of the groove  44 B to a height position corresponding to an upper end of the ridge  44 A will be defined as a height h 2  [mm] of the second pleats  44 . 
     The height h 1  is set to a height smaller than the height h 2 . In this embodiment, for example, the height h 1  is smaller than half of the height h 2 . To cause such a difference between the height h 1  and the height h 2 , one can process parts of a mold  70  for molding the liner  36  (see  FIG. 6A ) that respectively form the first pleats  42  and the second pleats  44  so as to adjust these parts to different heights. 
     The height h 1  is preset such that when the liner  36  is curved and then the curved liner  36  is heated while the inside of the liner  36  is pressurized, the first pleats  42  stretched out in the curving direction come into close contact with an inner circumferential surface of the fiber-reinforced part  52  on the inner side of the curve. 
     The height h 2  is preset such that when the liner  36  is curved and then the curved liner  36  is heated while the inside of the liner  36  is pressurized, the second pleats  44  stretched out in the curving direction come into close contact with an inner circumferential surface of the fiber-reinforced part  52  on the outer side of the curve. 
       FIG. 3A  shows the liner  36  before being curved, as seen from the Y-direction.  FIG. 3B  shows a horizontal section of the liner  36  cut along the X-Z plane at the center in the Y-direction. For example, the portions of the pleated part  38  on one side and the other side relative to the axis K are symmetrical as seen from the Y-direction. Therefore, only the portion on the one side as seen from the Y-direction will be described below while the description of the other portion will be omitted. 
     As shown in  FIG. 3B , the pleated part  38  as seen from the Y-direction has third pleats  46 . 
     The third pleats  46  have a plurality of ridges  46 A protruding from a center in the Z-direction of the third pleats  46  toward the fiber-reinforced part  52  (see  FIG. 4 ), and a plurality of grooves  46 B depressed from the center in the Z-direction toward the axis K. The ridges  46 A and the grooves  46 B are alternately arrayed in the X-direction. The pitch in the X-direction of the ridges  46 A and the pitch in the X-direction of the grooves  46 B have an equal length. In the Z-direction, the length from a height position corresponding to an inner end of the groove  46 B to a height position corresponding to an outer end of the ridge  46 A will be defined as a height h 3  [mm] of the third pleats  46 . 
     For example, the height h 3  shown in  FIG. 4  is set to a height smaller than the height h 2  and larger than the height h 1 . To set the height h 3  to such a height, one can process a part of the mold  70  for molding the liner  36  (see  FIG. 6A ) that forms the third pleats  46  so as to adjust this part to a different height. 
     An inner circumferential surface of the portion having the height h 1 , an inner circumferential surface of the portion having the height h 2 , and an inner circumferential surface of a portion having the height h 3  are formed such that these inner circumferential surfaces form a curved surface continuous in a circumferential direction of the pleated part  38 . In other words, in the inner circumferential surface of the pleated part  38 , the height in the R-direction is varied continuously in the circumferential direction, without any step formed in the inner circumferential surface of the pleated part  38 . Such a pleated structure is called an eccentric pleated structure. 
     Fiber-Reinforced Part 
     For example, the fiber-reinforced part  52  has an inner reinforcing layer  47  and an outer reinforcing layer  48 . 
     The inner reinforcing layer  47  is formed along the entire outer circumferential surface  38 A and outer circumferential surfaces  39 A (see  FIG. 2B ) in the X-direction so as to cover these outer circumferential surface  38 A and outer circumferential surfaces  39 A. For example, the inner reinforcing layer  47  is made of a carbon fiber-reinforced plastic (CFRP). For example, in the R-direction, the thickness of the inner reinforcing layer  47  is larger than the thickness of the liner  36 . The inner reinforcing layer  47  has an outer circumferential surface  47 A. 
     The outer reinforcing layer  48  is formed along the entire outer circumferential surface  47 A in the X-direction so as to cover the outer circumferential surface  47 A. For example, the outer reinforcing layer  48  is made of a glass fiber-reinforced plastic. For example, in the R-direction, the thickness of the outer reinforcing layer  48  is larger than the thickness of the inner reinforcing layer  47 . 
     Workings and Effects 
     Next, the manufacturing method of the high-pressure vessel  30  of the first embodiment will be described. 
     The mold  70  shown in  FIG. 6A  includes: a first corrugated part  72  that forms the first pleats  42 ; a second corrugated part  74  that forms the second pleats  44 ; a corrugated part (not shown) that forms the third pleats  46  (see  FIG. 3B ); and curved surface parts  76  that form the cylindrical parts  39 . The height in the Y-direction of the first corrugated part  72  is set according to the height h 1  (see  FIG. 4 ). The height in the Y-direction of the second corrugated part  74  is set according to the height h 2  (see  FIG. 4 ). The height in the Z-direction of the corrugated part (not shown) is set according to the height h 3  (see  FIG. 4 ). 
     Here, a molten resin is delivered into the mold  70 , and then air is delivered into the mold. As the resin is cooled, the liner  36  is molded. The molded liner  36  is taken out of the mold  70 . Thus, the resin liner  36  is molded, for example, by a blow molding method (an example of a step of molding a tubular body). The liner  36  has the pleated part  38  formed therein. 
     Then, as shown in  FIG. 5 , the fiber-reinforced part  52  is formed on an outer circumferential side of the molded liner  36  (an example of a step of forming a reinforcing part). More particularly, carbon fibers impregnated with an uncured resin are wound around the outer circumferential surface  36 A of the liner  36  (by braiding) to form the inner reinforcing layer  47 . Then, glass fibers impregnated with an uncured resin are wound around the outer circumferential surface  47 A of the inner reinforcing layer  47  to form the outer reinforcing layer  48 . In this way, the fiber-reinforced part  52  is formed on the outer circumferential side of the liner  36  (an example of the step of forming the reinforcing part). The liner  36  that has the fiber-reinforced part  52  formed on the outer circumferential side and that is not curved yet (the liner  36  having a linear shape) will be referred to as an unprocessed connecting part  62 . 
     Then, as shown in  FIG. 6B , the unprocessed connecting part  62  is curved such that part of the axis K of the unprocessed connecting part  62  draws a curved line. Thus, the liner  36  and the fiber-reinforced part  52  are curved (an example of a curving step). The unprocessed connecting part  62  is curved, for example, by fitting the unprocessed connecting part  62  into a U-shaped mold (not shown). As the unprocessed connecting part  62  is curved, the first pleats  42  on the inner side of the curve and the second pleats  44  on the outer side of the curve are each pulled in the curving direction (axial direction). 
     Then, as shown in  FIG. 6C , the curved liner  36  and fiber-reinforced part  52  are heated with a heater  84  while the inside of the liner  36  is pressurized with a compressor  82  (an example of a step of pressurizing and heating). To clearly show how the liner  36  and the fiber-reinforced part  52  are heated and pressurized, the mold is not shown and the heater  84  is only partially shown in  FIG. 6C . 
     Here, the liner  36  is subjected to a tensile force in the curving direction and the internal pressure of the liner  36  is raised by pressurization with the compressor  82 , so that the height of the first pleats  42  on the inner side of the curve and the height of the second pleats  44  on the outer side of the curve become smaller than those before curving. As a result, the clearance between the first pleats  42  and the fiber-reinforced part  52 , and the clearance between the second pleats  44  and the fiber-reinforced part  52  are reduced. In other words, the area of contact between the fiber-reinforced part  52  and the pleated part  38  is increased. The resin in the liner  36  and the resin in the fiber-reinforced part  52  are cured by heating. 
     Through these steps, the connecting part  34  is formed as shown in  FIG. 6D . The connecting part  34  is connected at one end and the other end in the axial direction by adhesion to the vessel main body  32 A and the vessel main body  32 B (see  FIG. 1 ) that have been separately formed. Thus, the vessel main body  32 A, the vessel main body  32 B, and the connecting part  34  are integrated. The other connecting parts  34  are connected to the other vessel main bodies  32  (see  FIG. 1 ) in the same manner to form the high-pressure vessel  30  (see  FIG. 1 ). 
     As has been described above, in the manufacturing method of the high-pressure vessel  30 , the height h 1  of the first pleats  42  is set to be smaller than the height h 2  of the second pleats  44 . This allows the first pleats  42  to be stretched out along the curving direction at the part of the liner  36  on the inner side of the curve when the liner  36  and the fiber-reinforced part  52  are curved. In other words, the clearance in the Y-direction between the ridges  42 A of the first pleats  42  and the fiber-reinforced part  52  is reduced. As a result, the area of contact between the first pleats  42  and the fiber-reinforced part  52  is increased and the degree of freedom for deformation of the first pleats  42  is reduced. Thus, this method can ensure that when the liner  36  and the fiber-reinforced part  52  are curved and then the inside of the curved liner  36  is pressurized (the high-pressure vessel  30  is used), the part of the liner  36  on the inner side of the curve is less prone to deformation. 
     As shown in  FIG. 7 , slight ridges remain at the portion corresponding to the first pleats  42  in the connecting part  34  of the high-pressure vessel  30  having been formed. However, the degree of close contact with the fiber-reinforced part  52  at the portion corresponding to the first pleats  42  and that at the portion corresponding to the second pleats  44  are equivalent. 
     Second Embodiment 
     Next, a high-pressure vessel  90  as an example of a pressure vessel according to a second embodiment and a manufacturing method of the high-pressure vessel  90  will be described. 
     The high-pressure vessel  90  shown in  FIG. 8  is provided in the vehicle  10  (see  FIG. 1 ) in place of the high-pressure vessel  30  (see  FIG. 1 ). Those components of the high-pressure vessel  90  that are basically the same as in the high-pressure vessel  30  will be denoted by the same reference signs as in the high-pressure vessel  30  while the description thereof will be omitted. For example, the high-pressure vessel  90  has five vessel main bodies  32  (see  FIG. 1 ) and four connecting parts  92  (see  FIG. 8 ). 
     The basic configuration of the connecting part  92  is the same as that of the connecting part  34  (see  FIG. 7 ). However, different conditions of pressurization are used in manufacturing, so that the portion of the connecting part  92  corresponding to the first pleats  42  (see  FIG. 5 ) of the connecting part  34  (see  FIG. 4 ) is different in shape from the first pleats  42 . 
     More particularly, a pressure higher than the pressure applied to the inside of the connecting part  34  (see  FIG. 6D ) in the first embodiment is used for pressurizing the unprocessed connecting part  62  (see  FIG. 6C ) to form the connecting part  92 . This pressure is adjusted by adjusting the pressure in the compressor  82  (see  FIG. 6C ) or changing the compressor  82 . The amount of the pressure is set such that the first pleats  42  after heating form a curved part extending along the fiber-reinforced part  52  as seen from the X-direction. In other words, the amount of the pressure is set such that the first pleats  42  after heating have a linear shape extending along the fiber-reinforced part  52  as seen from the Z-direction. 
     Workings and Effects 
     Next, the manufacturing method of the high-pressure vessel  90  of the second embodiment will be described. In the following, only differences from the manufacturing method of the high-pressure vessel  30  (see  FIG. 1 ) will be described while the description of the same steps will be omitted. 
     After the unprocessed connecting part  62  (see  FIG. 6C ) is curved, the inside of the curved liner  36  is pressurized with the compressor  82  (see  FIG. 6C ). Since the liner  36  is subjected to a tensile force in the curving direction and the internal pressure of the liner  36  is raised by pressurization with the compressor  82 , the height of the first pleats  42  on the inner side of the curve and the height of the second pleats  44  on the outer side of the curve become smaller than those before curving. 
     Here, the pressure applied to the inside of the liner  36  is higher than the pressure applied in the first embodiment, so that not only the second pleats  44  on the outer side of the curve but also the first pleats  42  on the inner side of the curve are deformed so as to extend along the fiber-reinforced part  52 . As a result, the clearance between the first pleats  42  and the fiber-reinforced part  52 , and the clearance between the second pleats  44  and the fiber-reinforced part  52  are reduced. In other words, the area of contact between the fiber-reinforced part  52  and the pleated part  38  is increased. The resin in the liner  36  and the resin in the fiber-reinforced part  52  are cured by heating. 
     Through these steps, the connecting part  92  shown in  FIG. 8  is formed. The connecting part  92  is connected at one end and the other end in the axial direction by adhesion to the vessel main body  32 A and the vessel main body  32 B (see  FIG. 1 ) that have been separately formed. Thus, the vessel main body  32 A, the vessel main body  32 B, and the connecting part  92  are integrated. The other connecting parts  92  are connected to the other vessel main bodies  32  in the same manner to form the high-pressure vessel  90 . 
     As has been described above, in the manufacturing method of the high-pressure vessel  90 , the height h 1  of the first pleats  42  (see  FIG. 5 ) is set to be smaller than the height h 2  of the second pleats  44  (see  FIG. 5 ). This allows the first pleats  42  to be stretched out along the curving direction at the part of the liner  36  on the inner side of the curve when the liner  36  and the fiber-reinforced part  52  are curved. In other words, the clearance in the Y-direction between the ridges  42 A of the first pleats  42  and the fiber-reinforced part  52  is reduced. As a result, the area of contact between the first pleats  42  and the fiber-reinforced part  52  is increased and the degree of freedom for deformation of the first pleats  42  is reduced. Thus, this method can ensure that when the liner  36  and the fiber-reinforced part  52  are curved and then the inside of the curved liner  36  is pressurized, the part of the liner  36  on the inner side of the curve is less prone to deformation. 
     In the manufacturing method of the high-pressure vessel  90 , a predetermined pressure is applied in the process of heating the liner  36  while pressurizing the inside of the liner  36 , so that not only the second pleats  44  on the outer side of the curve but also the first pleats  42  on the inner side of the curve are deformed so as to have a smaller height after heating. Moreover, the first pleats  42  after heating form a curved part extending along the fiber-reinforced part  52  as seen from the curving direction. Thus, applying the predetermined pressure to the first pleats  42  and the second pleats  44  can cause not only the second pleats  44  but also the first pleats  42  to assume a shape extending along the X-direction. As a result, the area of contact between the first pleats  42  and the fiber-reinforced part  52  is increased compared with when a low pressure is applied, and the clearance between the first pleats  42  and fiber-reinforced part  52  after heating can be reduced accordingly. 
     The present disclosure is not limited to the above-described embodiments. 
     The number of the vessel main bodies  32  is not limited to five but may be two or any number other than five that is not smaller than three. The number of the connecting parts  34 ,  92  is not limited to four but may be one or any number other than four that is not smaller than two. 
     The length in the X-direction of the pleated part  38  may be set to be equal to the length in the X-direction of the connecting parts  34 ,  92 . In other words, the entire connecting parts  34 ,  92  may be pleated. The length in the X-direction of the pleated part  38  is not limited to a length of about a quarter of the length in the X-direction of the connecting parts  34 ,  92 , and may be set to a length other than this quarter length and shorter than the length in the X-direction of the connecting parts  34 ,  92 . 
     The height h 1  in the Y-direction of the first pleats  42  may be set to an even smaller height while the same conditions of pressurization as in the first embodiment are used.  FIG. 9  shows a state where a height h 4  [mm] in the Y-direction of the first pleats  42  before curving is set to be smaller than the height h 1  (see  FIG. 4 ). Thus, setting the height of the first pleats  42  to an even smaller height can increase the area of contact between the portion of the first pleats  42  and the fiber-reinforced part  52  even when the conditions of pressurization are the same. 
     The height h 3  may be set to be equal to the height h 1  or the height h 2 . The height h 3  may be set to be smaller than the height h 2 . 
     The vessel main bodies  32  and the connecting parts  34 ,  92  are not limited to those that are molded as separate bodies and then connected to each other by adhesion, and these members may instead be integrally molded. 
     The fiber-reinforced part  52  is not limited to the one that has the inner reinforcing layer  47  and the outer reinforcing layer  48 , and the fiber-reinforced part  52  may instead have only either one of these layers. 
     The gas is not limited to the hydrogen gas G and may instead be another gas, such as oxygen or air. 
     While examples of the pressure vessel manufacturing method according to the embodiments and the modified examples of the present disclosure have been described above, it should be understood that these embodiments and modified examples may be combined as appropriate, and that the present disclosure can be implemented in various forms within the scope of the gist of the disclosure.