Abstract:
A coupling joint includes: joint member which has gear teeth; a center tube which has gear teeth meshing with the gear teeth, and through which a rotational force is transmitted between the joint member via the gear teeth and the gear teeth; a seal member which blocks a lubricated space including a meshing portion of the gear teeth and the gear teeth from the outside between the joint member and the center tube; a lubricant which fills the lubricated space; and a pressure-equalizing member which is provided to face a part of the lubricated space, changes the volume of the lubricated space by deforming in accordance with the pressure of the outside, and thereby equalizes the pressure of the lubricant and the pressure of the outside.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an underwater coupling joint and a water flow power generator. 
         [0002]    Priority is claimed on Japanese Patent Application No. 2015-028495, filed on Feb. 17, 2015, the content of which is incorporated herein by reference. 
       BACKGROUND ART 
       [0003]    A water flow power generator which performs power generation by using an ocean current or a water flow in the ocean or river includes an impeller and a power generator. The impeller has a plurality of blades which extend toward an outer circumferential side. An end portion of a rotational shaft is linked to the impeller, the rotational shaft rotates together with the impeller that rotates by the ocean current or the water flow, and thereby the power generator performs power generation. 
         [0004]    In the water, a large force generated by the ocean current or the water flow acts on the blades of the impeller. Then, a force or a moment in an axial direction or in a radial direction acts on the rotational shaft linked to the center of the impeller. 
         [0005]    In order to increase power generation efficiency, a method of increasing a diameter of the impeller, that is, a length of the blades, is employed. However, the force or the moment which acts on the rotational shaft from the impeller substantially increases. 
         [0006]    In order to prevent an influence caused by the above-described force or moment on the power generator from the impeller, there is a case where a coupling device described in Patent Document 1, for example, is used between the impeller and the rotational shaft of the power generator. The coupling device performs transmission of the rotational force between the impeller and the rotational shaft of the power generator while allowing a phase displacement in the axial direction, in the radial direction, and in the inclining direction of a side close to the impeller and a side close to the power generator. 
         [0007]    In the coupling device, since a gear is used in transmission of the rotational force, a lubricant for suppressing wear becomes necessary in a meshing portion of the gears. 
         [0008]    The coupling device described in Patent Document 1 includes a seal member in order to prevent a fluid having a high pressure from entering from the outside. 
       CITATION LIST 
     Patent Literature 
       [0009]    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2011-21619 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    In a case where an underwater power generator is installed being sunk deep in the sea, a high water pressure, for example, 30 atmospheric pressure (approximately 3 MPa) acts. Therefore, there is a possibility that the seawater flows into the underwater power generator from the outside through a seal portion by a seal member. In this case, there is a possibility that the lubricant of a meshing portion of the gear flows out. When the lubricant flows out, the gear is damaged due to an increase in friction of the meshing portion, and there is a possibility that the underwater power generator cannot be used. 
         [0011]    Meanwhile, in order to maintain sealing properties in the seal portion, a method of periodically performing exchange of the seal member or supply of the lubricant is considered. However, in this case, a load applied to maintenance increases. Furthermore, marine pollution caused by an outflow of the lubricant is also concerned. 
         [0012]    An object of the present invention is to provide an underwater coupling joint which can suppress a load applied to maintenance, and a water flow power generator. 
       Solution to Problem 
       [0013]    According to one aspect of the present invention, an underwater coupling joint includes a first shaft member which has first gear teeth. The underwater coupling joint further includes a second shaft member which has second gear teeth meshing with the first gear teeth, and through which a rotational force is transmitted between the first shaft members via the first gear teeth and the second gear teeth. The underwater coupling joint further includes a seal member which blocks a space including a meshing portion of the first gear teeth and the second gear teeth from the outside between the first shaft members and the second shaft member. The underwater coupling joint further includes a lubricant which fills the space. The underwater coupling joint further includes a pressure-equalizing mechanism which is provided to face a part of the space, changes the volume of the space by deforming in accordance with a pressure of the outside, and thereby equalizes the pressure of the lubricant and the pressure of the outside. 
         [0014]    In this configuration, when the underwater coupling joint is sunk in the water, it is possible to deform the pressure-equalizing mechanism in accordance with the pressure of the outside, that is, the periphery of the underwater coupling joint. 
         [0015]    By the deformation of the pressure-equalizing mechanism, it is possible to equalize the pressure of the lubricant in the space and the pressure of the outside by changing a volume of the space filled with the lubricant. Accordingly, it is possible to suppress generation of a large difference in pressure between the seal member and each of the first shaft member and the second shaft member. As a result, it is possible to suppress infiltration of water from the outside into the space filled with the lubricant, or leakage of the lubricant to the outside from the space. 
         [0016]    According to a second aspect of the invention, in the underwater coupling joint, the pressure-equalizing mechanism may be bellows of which a first end portion is open, the other end portion has a blocked tubular shape, and the first end portion and the other end portion are capable of extending and contracting in a direction of being in contact with and separated from each other. 
         [0017]    By using such bellows, it is possible to make the pressure of the outside act on the other blocked end. Accordingly, it is possible to shorten the bellows in a direction in which the other end approaches the opened first end portion. Furthermore, it is possible to extend the bellows in a direction in which the other end side is separated from the first end portion. Accordingly, the volume of the space changes, and it is possible to equalize each pressure of the water of the outside and the lubricant in the space. 
         [0018]    According to a third aspect of the invention, in the underwater coupling joint, the bellows in the second aspect may have a spiral groove on an inner circumferential surface. 
         [0019]    In this configuration, when filling the inside of the space with the lubricant, by rotating the bellows around a center shaft, it is possible to move bubbles that remain on the inner side of the groove along the spiral groove. Therefore, it is possible to discharge the bubbles that remain on the inner side of the groove from the first end portion of the opened bellows. 
         [0020]    According to a fourth aspect of the invention, in the underwater coupling joint, in any aspect of the first to third aspects, an external pressure introduction portion which introduces the pressure of the outside to the inside of one of the first shaft member and the second shaft member may be provided, and the external pressure introduction portion may include the pressure-equalizing mechanism. 
         [0021]    In this configuration, it is possible to make the pressure of the outside act on the pressure-equalizing mechanism via the external pressure introduction portion. Therefore, it is possible to equalize the pressure of the water of the outside and the lubricant in the space. 
         [0022]    By providing the external pressure introduction portion on the inside of one of the first shaft member and the second shaft member, it is possible to achieve efficient use of the space. Furthermore, by providing the pressure-equalizing mechanism in the external pressure introduction portion, the pressure-equalizing mechanism is not exposed to the outside, and it is possible to suppress damage of the pressure-equalizing mechanism by unexpected contact or the like. 
         [0023]    According to a fifth aspect of the invention, in the underwater coupling joint, in any aspect of the first to third aspects, an injection port through which the lubricant is injected from the outside into the space may be provided in one of the first shaft member and the second shaft member, and the injection port may include the pressure-equalizing mechanism. 
         [0024]    In this configuration, when the pressure-equalizing mechanism is provided in the injection port of the lubricant, the pressure of the outside acts on the pressure-equalizing mechanism via the injection port, and it is possible to achieve equalization of the pressure of the water of the outside and the lubricant in the space. Accordingly, it is not necessary to additionally provide a part for providing the pressure-equalizing mechanism. 
         [0025]    According to a sixth aspect of the invention, in the underwater coupling joint, in any aspect of the first to third aspects, the seal member may be formed to be deformable in accordance with the pressure of the outside, and may also function as the pressure-equalizing mechanism. 
         [0026]    In this manner, as the seal member functions as the pressure-equalizing mechanism, it is possible to reduce the number of components. 
         [0027]    According to a seventh aspect of the invention, in the underwater coupling joint, in any aspect of the first to sixth aspects, the seal member may be bonded to the first shaft member and the second shaft member. 
         [0028]    In this manner, by bonding the seal member to the first shaft member and the second shaft member, it is possible to suppress infiltration of water from the outside into the space filled with the lubricant, or leakage of the lubricant to the outside from the space. 
         [0029]    According to an eighth aspect of the invention, a water flow power generator includes: an impeller having a plurality of blades; a power generator which is driven by the impeller; and the above-described underwater coupling joint which links a rotational shaft of the impeller and an input shaft of the power generator. 
         [0030]    In this configuration, in the underwater coupling joint, it is possible to suppress infiltration of water from the outside into the space filled with the lubricant, or leakage of the lubricant to the outside from the space. 
       Advantageous Effects of Invention 
       [0031]    According to the above-described underwater coupling joint and the water flow power generator, it is possible to maintain a lubricated state in the underwater coupling joint, and to suppress a load applied to maintenance. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0032]      FIG. 1  is a perspective view showing a water flow power generator according to an embodiment of the invention. 
           [0033]      FIG. 2  is a sectional view showing a configuration of a linking part between an impeller and a nacelle in the embodiment of the water flow power generator. 
           [0034]      FIG. 3  is a sectional view showing a configuration of an underwater coupling joint in a first embodiment of the invention. 
           [0035]      FIG. 4  is a sectional view showing a configuration of an underwater coupling joint in a second embodiment of the invention. 
           [0036]      FIG. 5  is a sectional view showing a configuration of an underwater coupling joint in a third embodiment of the invention. 
           [0037]      FIG. 6  is a sectional view showing a configuration of an underwater coupling joint in a fourth embodiment of the invention. 
           [0038]      FIG. 7  is a sectional view showing a modification example of a seal member provided in the underwater coupling joint. 
           [0039]      FIG. 8  is a sectional view showing a modification example in which the seal member and bellows of a pressure-equalizing member have a spiral shape. 
           [0040]      FIG. 9  is a sectional view showing a modification example in which a meshing portion has a tapered shape. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0041]      FIG. 1  is a perspective view showing a water flow power generator according to an embodiment.  FIG. 2  is a sectional view showing a configuration of a linking part between an impeller and a nacelle in the embodiment of the water flow power generator. 
         [0042]    As shown in  FIG. 1 , a water flow power generator  10  in the embodiment is installed in the deep seawater by being moored via an anchor line (not shown), on the seabed or in an underwater structure. 
         [0043]    The water flow power generator  10  includes an impeller  20  and a nacelle  30 . 
         [0044]    The impeller  20  includes a hub  21  and a blade  22 . 
         [0045]    As shown in  FIGS. 1 and 2 , the hub  21  is disposed in a center portion of the impeller  20 . The hub  21  is formed in a so-called shell shape of which an outer diameter gradually decreases toward a tip end  21   a.  The hub  21  has an end surface  21   b  on a side opposite to the tip end  21   a.  The end surface  21   b  is orthogonal to a rotation center shaft C (hereinafter, simply referred to as a shaft line C) of the impeller  20 . In an outer circumferential portion of the end surface  21   b  of the hub  21 , a tubular portion  21   c  is integrally provided. The tubular portion  21   c  is formed in a cylindrical shape which extends toward the side opposite to the tip end  21   a  in a direction (hereinafter, simply referred to as a shaft line C direction) in which the shaft line C extends. On the end surface  21   b  of the hub  21 , a shaft (rotational shaft)  23  is integrally attached. The shaft  23  protrudes toward the side opposite to the tip end  21   a  in the shaft line C direction. 
         [0046]    A plurality of the blades  22  are provided at an interval in the circumferential direction in the outer circumferential portion of the hub  21 . 
         [0047]    In the embodiment, two blades  22  are provided. The two blades  22  are disposed at positions which are rotationally symmetric to each other. In each of the blades  22 , a base end portion  22   a  is integrally fixed to the tubular portion  21   c  of the hub  21 . Each of the blades  22  extends outward in a radiation direction from the hub  21  toward a tip end portion  22   b  thereof. 
         [0048]    The nacelle  30  includes a casing  31 , a power generator  32 , and a main shaft  33 . 
         [0049]    The casing  31  is formed in a cylindrical shape which extends in the shaft line C direction. In the casing  31 , an impeller support portion  34  is provided in a first end portion  31   a  thereof The impeller support portion  34  supports the impeller  20  to be freely rotatable. On the outer circumferential surface of the impeller support portion  34 , one pair of external bearings  35  is provided at an interval in the shaft line C direction. The impeller  20  is supported by the impeller support portion  34  to be freely rotatable via the external bearings  35 . Each of the external bearings  35  is formed of, for example, a resin, and functions as a so-called slide bearing which supports the impeller  20  considering the seawater on the periphery as a lubricant. 
         [0050]    In the casing  31 , a partition wall  36  is provided. The partition wall  36  has a plane which is orthogonal to the shaft line C and is oriented toward the side (hereinafter, simply referred to as a second end portion side) opposite to the first end portion  31   a  in the shaft line C direction. In the casing  31 , a tightly-closed power generator chamber  37  is formed further on the second end portion side than the partition wall  36  in the shaft line C direction. The inside of the power generator chamber  37  is an air atmosphere. In the power generator chamber  37 , the power generator  32  is stored. 
         [0051]    The power generator  32  includes an input shaft  32   a.  The input shaft  32   a  protrudes to the side close to the partition wall  36  along the shaft line C. The power generator  32  includes a rotor (not shown) provided to be integrated with the input shaft  32   a,  and a stator (not shown) which opposes the rotor. The power generator  32  generates power as the rotor rotates relatively to the stator together with the input shaft  32   a.  The power generated by the power generator  32  is supplied to the outside via a power-transmission line (not shown). 
         [0052]    A main shaft  33  is linked to the input shaft  32   a  of the power generator  32  via a speed increaser (not shown) and a brake (not shown). 
         [0053]    The main shaft  33  extends in the impeller support portion  34  through a shaft hole  36   h  formed in the partition wall  36 . A ring-like seal member  38  is provided between the main shaft  33  and the shaft hole  36   h.  The seal member  38  prevents infiltration of water into the power generator chamber  37  from the periphery of the main shaft  33 . 
         [0054]    A coupling joint (underwater coupling joint)  50  is provided between the main shaft  33  and the shaft  23  provided in the hub  21  of the impeller  20 . The main shaft  33  and the shaft  23  are connected to each other via the coupling joint  50 . 
         [0055]      FIG. 3  is a sectional view showing a configuration of the underwater coupling joint in a first embodiment. 
         [0056]    As shown in  FIG. 3 , the coupling joint  50  includes a center tube (second shaft member)  51 , a joint member (first shaft member)  52 , and a seal portion  60 A. The joint members  52  are respectively provided at both ends of the center tube  51 . 
         [0057]    The center tube  51  is formed in a tubular shape. In both end portions of the center tube  51 , inner gears  54  are integrally provided. The inner gears  54  are formed in a continuous annular shape along the outer circumferential surface of the center tube  51 . The inner gear  54  includes gear teeth (second gear teeth)  54   g  in the outer circumferential portion thereof Here, in the gear teeth  54   g,  the shape of the section of gear surface  54   t  formed in the outer circumferential portion is curved in a projected shape such that a center portion  54   b  is swollen toward the outer circumferential side with respect to both end portions  54   a  in the gear width direction along the shaft line C. 
         [0058]    The joint member  52  integrally includes two disk-like joint plates  55  and two tubular outer sleeves  56 . 
         [0059]    One of the two joint plates  55  is integrally linked to the main shaft  33 . The other one of the two joint plates  55  is integrally linked to the shaft  23 . 
         [0060]    The outer sleeve  56  is provided to be integrated with each of the joint plates  55 . The outer sleeve  56  is provided on a surface side which opposes the center tube  51  of the joint plate  55 . On the inner circumferential sides of the outer sleeves  56 , the inner gear  54  of the center tube  51  is disposed. The outer sleeve  56  has gear teeth (first gear teeth)  56   g  having a shape of spur teeth which meshes with the gear teeth  54   g  of the inner gear  54 . 
         [0061]    The joint member  52  can be relatively displaced in the shaft line C direction with respect to the center tube  51  as the gear teeth  54   g  curved in a projected shape and the gear teeth  56   g  having a shape of spur teeth mesh with each other. The joint members  52  can be displaced in a direction of being inclined to each other with respect to the shaft line C as the gear teeth  54   g  and the gear teeth  56   g  mesh with each other. 
         [0062]    In other words, the impeller  20  having the shaft  23  is allowed to be displaced relative to the shaft line C direction with respect to the main shaft  33 , and to be inclined to each other. 
         [0063]    The joint members  52  are respectively linked to the gear teeth  54   g  of both ends of the center tube  51 . Therefore, the shaft  23  is allowed to be eccentric to the main shaft  33  in the radial direction while maintaining a state where the center shaft of one joint member  52  is parallel to the center shaft of the other joint member  52 . 
         [0064]    The seal portions  60 A respectively include a seal member  61 A, an external pressure introduction portion  62 A, and a pressure-equalizing member (pressure-equalizing mechanism)  63 A. 
         [0065]    The seal member  61 A blocks a space between an outer circumferential surface  51   f  of the center tube  51  and the outer sleeves  56  positioned on the outer circumferential sides of both end portions of the center tube  51 , while maintaining water-tightness. The seal member  61 A is formed in a shape of bellows that can extend and contract in the shaft line C direction. The seal member  61 A is made of metal. A first end portion  61   a  of the seal member  61 A is bonded to the outer circumferential surface  51   f  of the center tube  51  by seal welding or friction bonding. Similarly, a second end portion  61   b  of the seal member  61 A is bonded to the outer sleeve  56  by seal welding or friction bonding. The seal members  61 A can be deformed in accordance with the relative displacement in the shaft direction, in the radial direction, and in the inclining direction of the shaft  23  with respect to the main shaft  33 , and can maintain the sealed state. 
         [0066]    The external pressure introduction portion  62 A includes a seawater introduction portion  64 A and an introduction hole  65 A. 
         [0067]    The seawater introduction portion  64 A is a columnar passage which extends along the center shaft of the external pressure introduction portion  62 A. 
         [0068]    The introduction hole  65 A is formed to penetrate the seawater introduction portion  64 A in the thickness direction thereof. 
         [0069]    The outside of the center tube  51  and the seawater introduction portion  64 A communicate with each other by the introduction hole  65 A. Accordingly, in a state where the water flow power generator  10  is sunk in the water, the seawater flows into the seawater introduction portion  64 A via the introduction hole  65 A. 
         [0070]    The pressure-equalizing member  63 A is made of metal and is formed in a shape of bellows. In the pressure-equalizing member  63 A, a first end portion  63   a  is blocked and a second end portion  63   b  is open. The pressure-equalizing members  63 A are respectively disposed in both end portions of the seawater introduction portion  64 A in the shaft line C direction. The second end portion  63   b  of the pressure-equalizing member  63 A is fitted to each other to block both end portions of the seawater introduction portion  64 A. The first end portion  63   a  of the pressure-equalizing member  63 A is a flat surface which is orthogonal to the center shaft of the center tube  51 . 
         [0071]    The outer sleeve  56  of the joint member  52  includes two injection ports  66  which allow an outer circumferential surface  56   a  and an inner circumferential surface  56   b  to communicate with each other. For example, when assembling the water flow power generator  10 , lubricant J is injected through the injection port  66  and fills a void S 1  formed by the joint plate  55 , the outer sleeve  56 , and the inner gear  54  of the joint member  52 , from the side close to the outer circumferential surface  56   a  of the outer sleeve  56 . The void S 1  communicates with a space S 3  in the seal member  61 A through a meshing portion S 2  of the gear teeth  54   g  and the gear teeth  56   g.  The void S 1  communicates with a space S 4  in the pressure-equalizing member  63 A. A lubricated space (space) S is configured of the void S 1 , the meshing portion S 2 , the space S 3 , and the space S 4 . The lubricant J fills the lubricated space S. The injection port  66  is blocked by mounting a cap (not shown), welding or the like after filling the inside with the lubricant J. 
         [0072]    In the seal portion  60 A having such a configuration, when the nacelle  30  of the water flow power generator  10  is sunk in the water, the seawater flows into the seawater introduction portion  64 A from the introduction hole  65 A. Then, a pressure P 1  of the seawater in the seawater introduction portion  64 A acts on the first end portion  63   a  of the pressure-equalizing member  63 A. The pressure-equalizing member  63 A extends and contracts in the direction in which the first end portion  63   a  approaches and is separated from the second end portion  63   b  such that the pressure P 1  of the seawater that acts on the first end portion  63   a  and a pressure P 2  of the lubricant J of the space S 4  in the pressure-equalizing member  63 A are balanced. For example, when an underwater depth of the nacelle  30  increases and the pressure P 1  of the seawater becomes higher than the pressure P 2  of the lubricant J, the pressure-equalizing member  63 A having a shape of bellows contracts such that the first end portion  63   a  approaches the second end portion  63   b.  Accordingly, the pressure PI of the seawater on the periphery of the nacelle  30  and the pressure P 2  of the lubricant J that fills the lubricated space S become equalized. 
         [0073]    According to the above-described first embodiment, when the coupling joint  50  is sunk in the water, the pressure-equalizing member  63 A is deformed in accordance with the pressure that acts from the seawater. Therefore, it is possible to equalize the pressure of the lubricated space S and the pressure of the outside. Accordingly, it is possible to suppress the action of the large pressure from the outside on the seal member  61 A. Therefore, it is possible to suppress infiltration of water from the outside into the lubricated space S filled with the lubricant J, or leakage of the lubricant J to the outside from the lubricated space S. 
         [0074]    As a result, it is possible to maintain the lubricated state in the coupling joint  50 , and to suppress a load applied to the maintenance. 
         [0075]    Furthermore, by providing the external pressure introduction portion  62 A on the inside of the center tube  51 , it is possible to achieve an efficient use of the space. By providing the pressure-equalizing member  63 A in the external pressure introduction portion  62 A, it is possible to suppress damage of the pressure-equalizing member  63 A caused by unexpected contact or the like without exposing the pressure-equalizing member  63 A to the outside. 
         [0076]    Furthermore, since the pressure-equalizing member  63 A is made of metal, it is possible to easily ensure sufficient strength. Accordingly, it is possible to suppress damage of the pressure-equalizing member  63 A caused by the high pressure P 1  of the seawater. 
         [0077]    Furthermore, since the pressure-equalizing member  63 A has a shape of bellows, it is possible to increase a fluctuation amount of a volume of the space S 4  on the inside as the first end portion  63   a  approaches and is separated from the second end portion  63   b.    
         [0078]    Accordingly, in a case where an installation depth of the water flow power generator  10  is deep, it is possible to contract the pressure-equalizing member  63 A in accordance with the pressure P 1  of the seawater that increases in accordance with the underwater depth. Accordingly, it is possible to easily achieve equalization with the pressure P 2  of the lubricant J. Therefore, compared to a case of sealing by an O-ring or the like, it is possible to ensure a larger adjustment margin. 
         [0079]    Furthermore, since the seal member  61 A is bonded to the outer sleeve  56  and the center tube  51 , it is possible to reduce infiltration of water from the outside into the lubricated space S filled with the lubricant J, or leakage of the lubricant J to the outside from the lubricated space S. 
       Second Embodiment 
       [0080]    Next, the underwater coupling joint and the water flow power generator in a second embodiment of the invention will be described based on the drawings. Since the second embodiment is different from the first embodiment only in a configuration of an external pressure introduction portion  62 B and a pressure-equalizing member  63 B, the same parts as those of the first embodiment will be given the same reference numerals, and overlapping descriptions will be omitted. 
         [0081]      FIG. 4  is a sectional view showing a configuration of the underwater coupling joint in a second embodiment of the invention. 
         [0082]    As shown in  FIG. 4 , the coupling joint  50  in the embodiment includes the center tube  51 , the joint member  52 , and a seal portion  60 B. 
         [0083]    The seal portion  60 B includes the seal member  61 A, the external pressure introduction portion  62 B, and the pressure-equalizing member (pressure-equalizing mechanism)  63 B. 
         [0084]    The seal member  61 A blocks a space between the outer circumferential surface  51   f  of the center tube  51  and the outer sleeves  56  positioned on the outer circumferential sides of both end portions of the center tube  51 , while maintaining water-tightness. 
         [0085]    The external pressure introduction portion  62 B includes a seawater introduction portion  64 B and an introduction hole  65 B. 
         [0086]    The seawater introduction portions  64 B are respectively formed to be continuous in the shaft line C direction across the joint plates  55  on both sides of the coupling joint  50  and the main shaft  33  bonded to each of the joint plates  55  and the shaft  23 . 
         [0087]    The introduction holes  65 B are respectively formed to penetrate the main shaft  33  and the shaft  23 . The main shaft  33 , the outside of the shaft  23 , and the seawater introduction portion  64 B communicate with each other by the introduction hole  65 B. 
         [0088]    The pressure-equalizing member  63 B is formed in a shape of metal bellows. In the pressure-equalizing member  63 B, the first end portion  63   a  side is blocked and the second end portion  63   b  side is open. The pressure-equalizing member  63 B is provided in the end portion of the seawater introduction portion  64 B while the second end portion  63   b  faces the void S 1 . 
         [0089]    In the seal portion  60 B having such a configuration, when the nacelle  30  of the water flow power generator  10  is sunk in the water, the seawater flows into the seawater introduction portion  64 B from the introduction hole  65 B. Then, the pressure of the seawater in the seawater introduction portion  64 B acts on the first end portion  63   a  of the pressure-equalizing member  63 B. When the underwater depth of the nacelle  30  increases and the pressure P 1  of the seawater becomes higher than the pressure P 2  of the lubricant J, the pressure-equalizing member  63 B having a shape of bellows contracts in the direction in which the first end portion  63   a  approaches the second end portion  63   b . Accordingly, the pressure P 1  of the seawater on the periphery of the nacelle  30  and the pressure P 2  of the lubricant J that fills the lubricated space S become equalized. 
         [0090]    According to the above-described second embodiment, the pressure of the outside acts on the pressure-equalizing member  63 B as the water of the outside is introduced into the external pressure introduction portion  62 B. Therefore, it is possible to equalize the pressure of the water of the outside and the lubricant J in the lubricated space S. 
         [0091]    Accordingly, it is possible to suppress the action of the large pressure from the outside on the seal member  61 A. Therefore, it is possible to suppress infiltration of water from the outside into the lubricated space S filled with the lubricant J, or leakage of the lubricant J to the outside from the lubricated space S. 
         [0092]    As a result, it is possible to maintain the lubricated state in the coupling joint  50 , and to suppress a load applied to the maintenance. 
         [0093]    Furthermore, by providing the external pressure introduction portions  62 B respectively on the inside of the joint member  52 , the main shaft  33 , and the shaft  23 , it is possible to achieve an efficient use of the space. 
         [0094]    Furthermore, by providing the pressure-equalizing member  63 B in the external pressure introduction portion  62 B, it is possible to suppress damage of the pressure-equalizing member  63 A caused by unexpected contact or the like without exposing the pressure-equalizing member  63 B to the outside. 
       Third Embodiment 
       [0095]    Next, a third embodiment of the underwater coupling joint and the water flow power generator according to the invention will be described. The third embodiment is different from the first embodiment only in a configuration of an external pressure introduction portion  62 C and a pressure-equalizing member  63 C. Therefore, the same parts as those of the first and second embodiments will be given the same reference numerals, and overlapping descriptions will be omitted. 
         [0096]      FIG. 5  is a sectional view showing a configuration of the underwater coupling joint in the third embodiment of the invention. 
         [0097]    As shown in  FIG. 5 , the coupling joint  50  in the embodiment includes the center tube  51 , the joint member  52 , and a seal portion  60 C. 
         [0098]    The seal portion  60 C includes the seal member  61 A, the external pressure introduction portion  62 C, and the pressure-equalizing member (pressure-equalizing mechanism)  63 C. 
         [0099]    The seal member  61 A blocks a space between the outer circumferential surface  51   f  of the center tube  51  and the outer sleeves  56  positioned on the outer circumferential sides of both end portions of the center tube  51 , while maintaining water-tightness. 
         [0100]    The external pressure introduction portion  62 C in the embodiment functions as the injection port  66  formed for injecting the lubricant J into the lubricated space S. The injection port  66  is formed in the outer sleeve  56  of the joint member  52 . 
         [0101]    The pressure-equalizing member  63 C is formed in a shape of bellows. The pressure-equalizing member  63 C is formed of metal. In the pressure-equalizing member  63 C, the first end portion  63   a  side is blocked and the second end portion  63   b  side is open. The pressure-equalizing member  63 C is provided in the injection port  66 . The pressure-equalizing member  63 C is provided such that the opened second end portion  63   b  is oriented toward the outer circumferential side of the outer sleeve  56 . The pressure-equalizing member  63 C also functions as a cap that blocks the injection port  66  after the injection of the lubricant J. 
         [0102]    In the seal portion  60 C having such a configuration, when the nacelle  30  of the water flow power generator  10  is sunk in the water, the seawater flows into the injection port  66  which is the external pressure introduction portion  62 C. Then, the pressure of the seawater in the seawater introduction portion  64 C acts on the first end portion  63   a  of the pressure-equalizing member  63 C. When the underwater depth of the nacelle  30  increases and the pressure P 1  of the seawater becomes higher than the pressure P 2  of the lubricant J, the pressure-equalizing member  63 C having a shape of bellows extends in the direction in which the first end portion  63   a  is separated from the second end portion  63   b . Accordingly, the pressure P 1  of the seawater on the periphery of the nacelle  30  and the pressure P 2  of the lubricant J that fills the lubricated space S become equalized. 
         [0103]    According to the above-described third embodiment, when the coupling joint  50  is sunk in the water, the pressure-equalizing member  63 C is deformed in accordance with the pressure P 1  of the seawater. Accordingly, the pressure of the lubricant J in the lubricated space S and the pressure of the outside are equalized. Therefore, it is possible to suppress the action of the high pressure from the outside on the seal member  61 A. Accordingly, it is possible to suppress infiltration of water from the outside into the lubricated space S filled with the lubricant J, or leakage of the lubricant J to the outside from the lubricated space S. 
         [0104]    As a result, it is possible to maintain the lubricated state in the coupling joint  50 , and to suppress a load applied to the maintenance. 
         [0105]    Furthermore, as the pressure-equalizing member  63 C is provided with the injection port  66  of the lubricant J, it is not necessary to additionally provide a part for providing the pressure-equalizing member  63 C. In other words, similar to the configurations of the above-described first and second embodiments, it is not necessary to form the introduction holes  65 A and  65 B and the seawater introduction portion  64 A and  64 B. Furthermore, the pressure-equalizing member  63 C functions as a cap that blocks the injection port  66 . 
         [0106]    As a result, it is possible to reduce the number of components that configure the seal portion  60 C, and to further reduce a possibility of leakage by reducing the number of locations having a possibility of generation of leakage. 
         [0107]    In the above-described first to third embodiments, the seal member  61 A has a shape of bellows that can extend and contract. However, the seal member  61 A may be replaced with other seal members, such as an O-ring. 
       Fourth Embodiment 
       [0108]    Next, a fourth embodiment of the underwater coupling joint and the water flow power generator according to the invention will be described. In the fourth embodiment which will be described hereinafter, the same parts as those of the first to third embodiments will be given the same reference numerals, and overlapping descriptions will be omitted. 
         [0109]      FIG. 6  is a sectional view showing a configuration of the underwater coupling joint in the fourth embodiment of the invention. 
         [0110]    As shown in  FIG. 6 , the coupling joint  50  in the embodiment includes the center tube  51 , the joint member  52 , and a seal portion  60 D. 
         [0111]    The seal portion  60 D includes a seal member  61 D. 
         [0112]    The seal members  61 D are formed in a shape of bellows that can extend and contract in the shaft line C direction. The seal members  61 D are made of metal and block a space between the outer circumferential surface  51   f  of the center tube  51  and the outer sleeves  56  positioned on the outer circumferential sides of both end portions of the center tube  51 , while maintaining water-tightness. 
         [0113]    The seal members  61 D are formed in a tapered shape in which the outer diameter gradually increases as approaching the outer sleeve  56 . In the seal member  61 D formed in a tapered shape in this manner, the pressure P 1  of the seawater also acts in the shaft direction of the center tube  51 . 
         [0114]    In the embodiment, the seal member  61 D functions as a pressure-equalizing member  63 D (pressure-equalizing mechanism). In other words, when the nacelle  30  of the water flow power generator  10  is sunk in the water, the seal member  61 D is slightly pressed in the shaft direction by the pressure P 1  of the seawater that acts on the seal member  61 D, and for example, contracts in the direction in which the first end portion  61   a  approaches the second end portion  61   b.  Accordingly, the pressure P 1  of the seawater on the periphery of the nacelle  30  and the pressure P 2  of the lubricant J in a lubricated space S 5  in the seal member  61 D become equalized. 
         [0115]    According to the above-described fourth embodiment, the seal member  61 D can be deformed in accordance with the pressure of the outside, and functions as the pressure-equalizing member  63 D. 
         [0116]    Accordingly, similar to the configuration described in the above-described first and second embodiments, it is not necessary to form the introduction holes  65 A and  65 B and the seawater introduction portions  64 A and  64 B, or to provide the pressure-equalizing members  63 A to  63 C. 
         [0117]    As a result, it is possible to reduce the number of components that configure the seal portion  60 D. Furthermore, it is possible to further reduce a possibility of leakage by reducing the number of locations having a possibility of leakage. 
         [0118]    Similar to the above-described first embodiment, when the coupling joint  50  is sunk in the water, the seal member  61 D is deformed in accordance with the pressure P 1  of the seawater. Therefore, it is possible to equalize the pressure P 2  of the lubricant J in the lubricated space S and the pressure P 1  of the outside. Accordingly, it is possible to suppress the action of the high pressure from the outside on the seal member  61 D. As a result, it is possible to suppress infiltration of water from the outside into the lubricated space S filled with the lubricant J, or leakage of the lubricant J to the outside from the lubricated space S. 
         [0119]    In the above-described fourth embodiment, the seal member  61 D has a shape of bellows, but the shape thereof is not limited thereto. When the volume on the inner side of the seal member  61 D changes in accordance with the pressure PI of the seawater, any configuration may be used. 
         [0120]    For example, as shown in  FIG. 7 , the outer diameter of the bellows-like seal member  61 D may be gradually enlarged in the direction in which the pressure P 1  of the seawater acts, and a pressure receiving surface  70  which receives the pressure P 1  of the seawater may be provided. 
         [0121]    By the configuration, it is possible to efficiently perform extension and contraction deformation of the seal member  61 D by the pressure P 1  of the seawater. In this manner, the configuration in which the outer diameter is gradually enlarged can also be similarly employed in the pressure-equalizing members  63 A to  63 C. 
       Other Modification Examples 
       [0122]    The invention is not limited to the above-described embodiments, and includes embodiments obtained by adding various changes into the above-described embodiments within a scope that does not depart from spirit of the invention. In other words, specific shapes or configurations described in the embodiments are merely examples, and can be appropriately changed. 
         [0123]    In the first to third embodiments, the bellows-like seal member  61 A and the pressure-equalizing members  63 A to  63 C are used. However, the outer diameters of the bellow-like seal member  61 A and the pressure-equalizing members  63 A to  63 C may be gradually enlarged in the direction in which the pressure P 1  of the seawater acts. 
         [0124]    As shown in  FIG. 8 , the seal members  61 A and  61 D and the pressure-equalizing members  63 A to  63 C may be formed in a shape of bellows, and a groove  80  formed on the inner circumferential surface may be formed in a spiral shape. In the configuration, it is possible to easily discharge bubbles K which remain in the groove  80  when injecting the lubricant J by rotating the seal members  61 A and  61 D and the pressure-equalizing members  63 A to  63 C around each of the center shafts. Here, the seal members  61 A and  61 D and the pressure-equalizing members  63 A to  63 C are rotated such that the bubbles K move to the injection port  66  side along the groove  80 . Accordingly, it is possible to guide the bubbles K discharged from the seal members  61 A and  61 D and the pressure-equalizing members  63 A to  63 C to the injection port  66 , and to discharge the bubbles to the outside through the injection port  66  (refer to  FIG. 3 ). 
         [0125]    In a case where the bubbles K remain, even when the pressure-equalizing members  63 A to  63 C and the seal member  61 D contract due to the pressure P 1  of the seawater, the bubbles having lower density than that of the lubricant J are broken, and thus, the pressure P 2  of the lubricant J does not efficiently increase. However, by discharging the bubbles K as described above, it is possible to efficiently equalize the pressure P 1  of the seawater and the pressure P 2  of the lubricant J. 
         [0126]    Furthermore, as shown in  FIG. 9 , the seal members  61 A and  61 D having the spiral groove  80  may be mounted on the outer sleeve  56  having a tapered inner circumferential surface  56   c.  By doing so, it is possible to allow the bubbles escaped from the seal members  61 A and  61 D to smoothly pass through the meshing portion S 2 , and to move the bubbles to the injection port  66  side. Therefore, it is possible to further reduce residuals of the bubbles K. 
         [0127]    In each of the above-described embodiments and in each of the modification examples, a case where the water flow power generator  10  is installed in the deep sea is described, but the installation place is not limited to the deep sea. 
         [0128]    When the number of blades  22  of the impeller  20  is a plural number, the number is not limited to the above-described number. 
         [0129]    In addition to this, for example, as configurations of each portion of the water flow power generator  10 , other appropriate configurations can be employed. 
       INDUSTRIAL APPLICABILITY 
       [0130]    The invention can be employed in the underwater coupling joint and the water flow power generator. The underwater coupling joint and the water flow power generator in which the invention is employed can maintain a lubricated state in the underwater coupling joint and suppress a load applied to maintenance. 
       REFERENCE SIGNS LIST 
       [0131]      10  Water Flow Power Generator 
         [0132]      20  Impeller 
         [0133]      21  Hub 
         [0134]      21   a  Tip End 
         [0135]      21   b  End Surface 
         [0136]      21   c  Tubular Portion 
         [0137]      22  Blade 
         [0138]      22   a  Base End Portion 
         [0139]      22   b  Tip End Portion 
         [0140]      23  Shaft (Rotational Shaft) 
         [0141]      30  Nacelle 
         [0142]      31  Casing 
         [0143]      31   a  First End Portion 
         [0144]      31   b  Second End Portion 
         [0145]      32  Power Generator 
         [0146]      32   a  Input Shaft 
         [0147]      33  Main Shaft 
         [0148]      33   a  First End Portion 
         [0149]      33   b  Second End Portion 
         [0150]      34  Impeller Support Portion 
         [0151]      35  External Bearing 
         [0152]      36  Partition Wall 
         [0153]      36   h  Shaft Hole 
         [0154]      37  Power Generator Chamber 
         [0155]      38  Seal Member 
         [0156]      50  Coupling Joint (Underwater Coupling Joint) 
         [0157]      51  Center Tube (Second Shaft Member) 
         [0158]      51 F Outer Circumferential Surface 
         [0159]      52  Joint Member (First Shaft Member) 
         [0160]      54  Inner Gear 
         [0161]      54   a  End Portion 
         [0162]      54   b  Center Portion 
         [0163]      54   g  Gear Teeth 
         [0164]      54   t  Gear Surface 
         [0165]      55  Joint Plate 
         [0166]      56  Outer Sleeve 
         [0167]      56   a  Outer Circumferential Surface 
         [0168]      56   b  Inner Circumferential Surface 
         [0169]      56   g  Gear Teeth (First Gear Teeth) 
         [0170]      56   v  Inner Circumferential Surface 
         [0171]      60 A,  60 B,  60 C,  60 D Seal Portion 
         [0172]      61 A,  61 D Seal Member 
         [0173]      61   a  First End Portion 
         [0174]      61   b  Second End Portion 
         [0175]      62 A,  62 B,  62 C External Pressure Introduction Portion 
         [0176]      63 A,  63 B,  63 C,  63 D Pressure-Equalizing Member (Pressure-Equalizing Mechanism) 
         [0177]      63   a  First End Portion 
         [0178]      63   b  Second End Portion 
         [0179]      64 A,  64 B,  64 C Seawater Introduction Portion 
         [0180]      65 A,  65 B Introduction Hole 
         [0181]      65   a  First End Portion 
         [0182]      65   b  Second End Portion 
         [0183]      66  Injection Port 
         [0184]      67  Cap 
         [0185]      70  Pressure Receiving Surface 
         [0186]      80  Groove 
         [0187]    J Lubricant 
         [0188]    P 1  Pressure of Seawater 
         [0189]    P 2  Pressure of Lubricant 
         [0190]    S Lubricated Space (Space) 
         [0191]    S 1  Void 
         [0192]    S 2  Meshing Portion 
         [0193]    S 3  Space 
         [0194]    S 4  Space 
         [0195]    S 5  Lubricated Space