Patent Publication Number: US-11047399-B2

Title: Accumulator

Description:
TECHNICAL FIELD 
     The present invention relates to a metal bellows-type accumulator used as a pressure accumulator, a pulsation damper, and the like in, for example, automobile hydraulic systems and industrial equipment hydraulic systems. 
     BACKGROUND ART 
     An accumulator for pressure accumulation, pulsation damping (or buffering), and the like is provided in a hydraulic circuit of a hydraulic controller in, for example, automobiles and industrial equipment. Such an accumulator has a housing and a bellows arranged in the housing, the bellows comprising a metal bellows main body with a fixed end welded and fixed to the housing and a bellows cap mounted to the other end of the bellows main body. The bellows main body and the bellows cap cooperatively partition the interior space of the housing into a gas chamber for gas enclosure and a liquid chamber in communication with a fluid outflow and inflow path to be connected to the hydraulic circuit in a tightly closed manner. The bellows is also configured to operate in a pressure accumulating manner, a pulsation damping manner, and the like in which the bellows main body expands and contracts such that the gas pressure within the gas chamber and the liquid pressure within the liquid chamber are balanced upon receiving liquid flowing from the hydraulic circuit through the fluid outflow and inflow path into the liquid chamber. 
     In the accumulator disclosed in Patent Citation 1, a bellows mechanism is arranged within a housing consisting of a lid body and an outer shell member, and one end of a metal bellows of the bellows mechanism is welded and fixed to the interior surface portion of the metal lid body, which is provided with a fluid outflow and inflow path. An outer peripheral portion of the lid body is also welded and fixed, with the metal bellows being welded and fixed thereto, to a curved portion formed in an opening portion of the metal outer shell member, and the opening portion of the outer shell member is closed by the lid body, such that the bellows mechanism partitions the interior space of the housing into a gas chamber and a liquid chamber in a tightly closed manner. 
     CITATION LIST 
     Patent Literature 
     Patent Citation 1: JP 2010-174985 A (Page 3, FIG. 1) 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in Patent Citation 1, since the lid body, to which one end of the metal bellows of the bellows mechanism is welded and fixed, is welded and fixed to close the opening portion of the outer shell member with being pressed against the outer shell member, not only the operation of fixation is cumbersome, but also the lid body and the outer shell member cannot be separated easily. This means that there is a problem that it is difficult to maintain the bellows mechanism arranged within the housing. 
     The present invention has been made in view of the above-described problem, and an object thereof is to provide an accumulator for easier maintenance of a metal bellows. 
     Solution to Problem 
     In order to solve the foregoing problems, an accumulator according to a first aspect of the present invention includes a housing having a shell provided with an opening portion and a base body formed in a disk shape, a bellows made of metal and having an outer diameter smaller than an inner diameter of the opening portion. One end portion of the bellows is welded and fixed to the base body. An interior of the housing is partitioned into an inner space and an outer space of the bellows in a tightly closed manner. The base body has an outer diameter greater than the outer diameter of the bellows, and the base body is fixed detachably to the shell. 
     According to the first aspect, since the opening portion of the shell is formed to have an inner diameter smaller than the outer diameter of the bellows and the base body is formed to have an outer diameter greater than the outer diameter of the bellows, the bellows and the base body can be mounted to the shell by inserting the bellows welded and fixed to the base body through the opening portion of the shell and fixing the base body detachably to the shell, and further the bellows and the base body can be drawn and detached together through the opening portion of the shell for easier maintenance of the metal bellows. 
     In the accumulator according to a second aspect of the present invention, an inner peripheral surface of the shell is provided with a restrictive stepped portion with which an outer peripheral portion of the base body is in contact. 
     According to the second aspect, the outer peripheral portion of the base body comes into contact with the restrictive stepped portion provided in the inner peripheral surface of the shell, whereby the movement of the base body in the direction of insertion within the shell can be restricted and thereby the base body can be positioned easily with respect to the shell. 
     The accumulator according to a third aspect of the present invention further including an annular seal member provided between the outer peripheral portion of the base body and the inner peripheral surface of the shell, and a fixing member formed as a discrete body separate from the base body and configured to fix the base body to the shell. 
     According to the third aspect, when the base body is mounted to the shell, the annular seal member can be interposed between the outer peripheral portion of the base body and the inner peripheral surface of the shell, which can prevent fluid within the housing from leaking out. In addition, the fixing member formed as a discrete body separate from the base body can provide fixation with the outer peripheral portion of the base body in contact with and positioned with respect to the restrictive stepped portion provided in the inner peripheral surface of the shell, whereby the base body can be fixed in a predetermined position to the shell. That is, with this arrangement, the sealing function and the fixing function are adjusted independently and therefore can be fulfilled reliably without welding. 
     In the accumulator according to a fourth aspect of the present invention, the fixing member has an outer peripheral portion provided with a male screw portion screwed into a female threaded portion provided in the inner peripheral surface of the shell. 
     According to the fourth aspect, the base body can be fixed easily to the shell with the fixing member by screwing the male screw portion provided on the outer peripheral portion of the fixing member into the female threaded portion provided in the inner peripheral surface of the shell. 
     In the accumulator according to a fifth aspect of the present invention, the fixing member is annular. 
     According to the fifth aspect, since the fixing member is annular, the base body can be fixed evenly to the shell and the total weight can be reduced. 
     In the accumulator according to a sixth aspect of the present invention, the base body is provided with a through hole in communication with the inner space of the bellows. 
     According to the sixth aspect, since fluid can flow into or out of the inner space of the bellows through the through hole provided in the base body, the base body can be used as an oil port or a gas port. 
     In the accumulator according to a seventh aspect of the present invention, the base body is key-fitted into the shell. 
     According to the seventh aspect, the base body is key-fitted into the shell, whereby the base body can be prevented from being rotated with respect to the shell, which prevents the annular seal member from being rotated, even when the fixing member is screwed and thereby the base body is fixed to the shell, and allows a sealing performance of the annular seal member to be ensured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view showing a first embodiment of the accumulator according to the present invention. 
         FIG. 2  is a cross-sectional view showing a state where a seal member and a seal surface of the accumulator shown in  FIG. 1  are in close contact with each other. 
         FIG. 3  is a cross-sectional view showing a method of fixation of an oil port member to a shell using a fixing member in the first embodiment. 
         FIG. 4  is a cross-sectional view snowing a second embodiment of the accumulator according to the present invention. 
         FIG. 5  is a cross-sectional view showing a third embodiment of the accumulator according to the present invention. 
         FIG. 6  is a cross-sectional view showing a fourth embodiment of the accumulator according to the present invention. 
         FIG. 7  is a cross-sectional view showing a fifth embodiment of the accumulator according to the present invention. 
         FIG. 8  is a cross-sectional view of an inward gas-type accumulator which is shown as an embodiment of the accumulator according to the present invention and in which a liquid chamber is set on the outside of a bellows, while a gas chamber is set on the inside of the bellows. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Modes for carrying out an accumulator according to the present invention will hereinafter be described based on the following embodiments. 
     First Embodiment 
     The first embodiment of the accumulator according to the present invention will be described with, reference to  FIGS. 1 to 3 . The following description is based on the vertical and horizontal directions when viewed on the frontal side (front side) of the accumulator, which is on the near side of the plane of paper of  FIG. 1 . 
     The accumulator  1  is used as a pressure accumulator, a pulsation damper, and the like in, for example, automobile hydraulic systems and industrial equipment hydraulic systems, being a metal bellows-type accumulator in which a metal bellows is used as a bellows main body  31 . 
     As shown in  FIG. 1 , the accumulator  1  includes a housing  2  and a bellows  3  provided within the housing  2 . It is noted that  FIG. 1  shows a state where the bellows main body  31  to be described hereinafter expands due to a pressure by, for example, liquid accumulation. 
     The structure of the bellows  3  will first be described, in detail. As shown in  FIGS. 1 and 2 , the bellows  3  includes the metal bellows main body  31  having an approximately cylindrical shape with the upper and lower ends thereof opened and a disk-shaped metal bellows cap  32 . It is noted that the bellows main body  31  is formed to have an outer diameter D 1  smaller than the inner diameter d 2  on the upper end side of a cylindrical portion  42  of a shell  4  and the inner diameter d 4  of an opening portion  4   a  of the shell  4  to be described hereinafter (D 1 &lt;d 2 , d 4 ; see  FIG. 1 ). 
     The bellows main body  31  is welded and fixed to the interior surface portion (particularly corresponding to a welded portion  54   a  of a second annular convex portion  54 ) of an oil port member  5  (also referred to as a base body) to be described hereinafter so that a fixed end  31   a  forming the lower end is closed, while a lower surface  32   a  of the bellows cap  32  is welded and fixed, with an annular protection ring  33  sandwiched therebetween to close a freely movable end  31   b  forming the upper end. 
     It is noted that the protection ring  33  protects the bellows main body  31  not to come into direct contact with the inner peripheral surface  42   a  on the upper end side of the cylindrical portion  42  of the shell  4 , in which the outer peripheral surface  33   a  of the protection ring  33  and the inner peripheral surface  42   a  of the cylindrical portion  42  of the shell  4  are separated slightly in the radial direction for smooth sliding without interference with the expanding and contracting operation of the bellows  3 . 
     In addition, an annular seal holder  34  having a crank shape in cross-sectional view is fitted in the lower surface  32   a  of the bellows cap  32 , and a disk-shaped seal member  35  is attached and fixed to the seal holder  34 . 
     The seal member  35  is formed through adherence (e.g. vulcanizing adhesion) of a rubber elastic body  37  to part or all of the surface of a disk-shaped metal base material  36 . 
     The structure of the housing  2  will next be described in detail. As shown in  FIGS. 1 and 2 , the housing  2  is constituted by the bottomed cylindrical shell  4  having the opening portion  4   a  at the lower end and the oil port member  5  for sealing the opening portion  4   a  of the shell  4 . It is noted that the oil port member  5  is fixed, while sealing the opening portion  4   a  of the shell  4 , to the shell  4  with a separate fixing member  6 . 
     A gas enclosure port  40  for injecting high-pressure gas (e.g. nitrogen gas) therethrough into a gas chamber  7  to be described hereinafter formed within the housing  2  is provided at an approximately radially central position of an upper end portion of the shell  4 . It is noted that the gas enclosure port  40  is closed with a gas plug  41  screwed and fixed therein after injection of high-pressure gas. Upon this, an O-ring  41   a  composed of a rubber elastic body and interposed between the gas plug  41  and the shell  4  can prevent high-pressure gas within the gas chamber  7  of the housing  2  from leaking out. 
     Further, the cylindrical portion  42  of the shell  4  is configured such that the opening portion  4   a  is thickened radially outward, a first annular recessed portion  43  to which the oil port member  5  is mounted is formed in the inner peripheral surface  43   a  closer to the opening portion  4   a  than the inner peripheral surface  42   a  on the upper end side of the cylindrical portion  42 , and a second annular recessed portion  44  to which the fixing member  6  is mounted is formed in the inner peripheral surface  44   a  closer to the opening portion  4   a  than the first annular recessed portion  43  (or the inner peripheral surface  43   a ). 
     The first annular recessed portion  43  is formed to have an inside diameter d 3  greater than the inner diameter d 2  of the inner peripheral surface  42   a  on the upper end side of the cylindrical portion  42  of the shell  4  (against which the outer peripheral surface  33   a  of the protection ring  33  of the above-described bellows  3  slides) (d 2 &lt;d 3 ; see  FIG. 1 ). This causes a radially annular face portion to be formed between an end portion on the opening portion  4   a  side of the inner peripheral surface  42   a  of the cylindrical portion  42  of the shell  4  and an end portion on the upper end side of the first annular recessed portion  43  (or the inner peripheral surface  43   a ) due to the dimensional difference between the inner diameter d 2  of the inner peripheral surface  42   a  on the upper end side of the cylindrical portion  42  and the inner diameter d 3  of the first annular recessed portion  43 , whereby an approximately right-angled first annular stepped portion  45  (restrictive stepped portion) is formed in the cylindrical portion  42  of the shell  4 . 
     The second annular recessed portion  44  is formed to have an inside diameter d 4  greater than the inside diameter d 3  of the first annular recessed portion  43  (d 3 &lt;d 4 ; see  FIG. 1 ). It is noted that the inner diameter d 4  of the second annular recessed portion  44  is approximately equal to the inner diameter d 4  of the opening portion  4   a  of the shell  4 . This causes a radially annular face portion to be formed between an end portion on the opening portion  4   a  side of the first annular recessed portion  43  (or the inner peripheral surface  43   a ) of the cylindrical portion  42  of the shell  4  and an end portion on the upper end side of the second annular recessed portion  44  (or the inner peripheral surface  44   a ) due to the dimensional difference between the inner diameter d 3  of the first annular recessed portion  43  and the inner diameter d 4  of the second annular recessed portion  44 , whereby an approximately right-angled second annular stepped portion  46  is formed in the cylindrical portion  42  of the shell  4 . The second annular recessed portion  44  is also formed with a female threaded portion  44   b  into which a male screw portion  61   b  formed on the fixing member  6  to be described hereinafter is screwed. 
     The oil port member  5  is provided with a fluid outflow and inflow path  50  (also referred to as a through hole) penetrating in the axial direction thereof within the housing  2  through which liquid (e.g. hydraulic oil) flows out of and into pressure piping not shown. 
     The oil port member  5  is also provided with an annular mounting portion  51  with an outer diameter D 3  approximately equal to the inner diameter d 3  of the first annular recessed portion  43  formed in the cylindrical portion  42  of the shell  4 , and an O-ring  52  (also referred to as an annular seal member) composed of a rubber elastic body is mounted in an annular groove portion  51   b  formed in the outer peripheral surface  51   a  of the mounting portion  51  and recessed radially inward. It is noted that the mounting portion  51  is formed to have an outer diameter D 3  greater than the outer diameter D 1  of the bellows main body  31  (D 1 &lt;D 3 ; see  FIG. 1 ). 
     The interior surface (i.e. an upper surface) of the oil port member  5  is also formed with a first annular convex portion  53  protruding upward (toward the interior of the housing  2 ) from the mounting portion  51  and having an outer diameter D 2  approximately equal to the inner diameter d 2  of the inner peripheral surface  42   a  on the upper end side of the cylindrical portion  42  of the shell  4 , and a second annular convex portion  54  protruding upward is formed on the radially inside of the first annular convex portion  53 , to which the fixed end  31   a  of the above-described bellows main body  31  is welded and fixed. Further, a third annular convex portion  55  protruding upward is formed on the radially inside of the second annular convex portion  54 , and a stay  56  having an approximately inverse U shape in cross-sectional view is welded and fixed on the radially outside. 
     A through hole  56   a  penetrating in the axial direction is provided at an approximately radially central position of an upper end portion of the stay  56 , and an annular seal surface  56   b  is formed on the radially outside of the through hole  56   a.    
     The interior space of the housing  2  has a structure partitioned by the bellows  3  (including bellows main body  31  and bellows cap  32 ) into a gas chamber  7  in communication with the gas enclosure port  40  and a liquid chamber  8  in communication with the fluid outflow and inflow path  50  in a tightly closed manner. 
     The gas chamber  7  is defined by the inner peripheral surface  42   a  of the shell  4 , the outer peripheral surface  31   c  of the bellows main body  31 , and the upper surface  32   b  of the bellows cap  32  to enclose high-pressure gas injected through the gas enclosure port  40 . 
     The liquid chamber  8  is defined by the stay  56 , the inner peripheral surface  31   d  of the bellows main body  31 , and the lower surface  32   a  of the bellows cap  32  (seal holder  34 , seal member  35 ), out of and into which liquid is to flow from the pressure piping through the fluid outflow and inflow path  50 . 
     The accumulator  1  performs pressure regulation through expanding and extracting operations of the bellows  3  provided within the housing  2  to move the bellows cap  32  to a predetermined position for balancing between the gas pressure within the gas chamber  7  and the liquid pressure within the liquid chamber  8 . 
     For example, as shown in  FIG. 2 , when liquid within the pressure piping is discharged, the bellows cap  32  moves downward under the gas pressure within the gas chamber  7  and thus the bellows main body  31  contracts, whereby the seal member  35  attached to the lower surface  32   a  of the bellows cap  32  and the seal surface  56   b  of the stay  56  come into close contact with each other to form an annular seal portion S 1  (see  FIG. 2 ) and close the through hole  56   a  of the stay  56 . This causes part of the liquid to be confined within the liquid chamber  8  and the pressure of the confined liquid and the gas pressure within the gas chamber  7  to be balanced, whereby the bellows main body  31  cannot be subject to an excessive stress and can be less likely to be damaged. 
     The structure of the fixing member  6  will next be described in detail. As shown in  FIGS. 1 and 2 , the fixing member  6  has an annular configuration with a through hole  60  penetrating in the axial direction provided on the radially inside, and a male screw portion  61   b  is formed on the outer peripheral surface  61   a  of the mounting portion  61  formed to have an outer diameter D 4  approximately equal to the inner diameter d 4  of the second annular recessed portion  44  that is formed in the cylindrical portion  42  of the shell  4 . It is noted that the tip of the mountain of the male screw portion  61   b  formed on the fixing member  6  is formed to have an outer diameter approximately equal to the inner diameter at the bottom of the valley of the female threaded portion  44   b  of the second annular recessed portion  44  formed in the cylindrical portion  42  of the shell  4 . 
     Also, on the upper surface of the fixing member  6  is formed an annular convex portion  62  protruding upward (toward the oil port member  5 ) from the mounting portion  61  and formed to have an outer diameter D 3  approximately equal to the inner diameter d 3  of the first annular recessed portion  43  formed in the cylindrical portion  42  of the shell  4 . 
     There will be described in detail a method for fixing the oil port member  5  to the shell  4  with the fixing member  6 . As shown in  FIG. 3 , the oil port member  5  with the fixed end  31   a  of the bellows main body  31  welded and fixed thereto is first inserted through the opening portion  4   a  of the shell  4  so that the bellows main body  31  is arranged within the shell  4 . Specifically, the interior surface (i.e. the upper surface) of the mounting portion  51  of the oil port member  5  is brought into contact with the first annular stepped portion  45  formed in the cylindrical portion  42  of the shell  4  and fitted into the first annular recessed portion  43 , so that the oil port member  5  is positioned axially with respect to the shell  4 . Upon this, the O-ring  52  is interposed between the outer peripheral surface  51   a  of the mounting portion  51  of the oil port member  5  and the first annular recessed portion  43  to form an annular seal portion S 2  (see  FIGS. 1 and 2 ). 
     Next, the male screw portion  61   b  formed on the outer peripheral surface  61   a  of the mounting portion  61  of the fixing member  6  is screwed into the female threaded portion  44   b  of the second annular recessed portion  44  formed in the cylindrical portion  42  of the shell  4 . Upon this, the annular convex portion  62  of the fixing member  6  presses the outer surface (i.e. lower surface) of the mounting portion  51  of the oil port member  5 , whereby the outer peripheral portion of the mounting portion  51  of the oil port member  5  can be fixed in a manner sandwiched between the first annular stepped portion  45  of the shell  4  and the annular convex portion  62  of the fix member  6 . Further, since the axial movement of the oil port member  5  with respect to the shell  4  is restricted by the first annular stepped portion  45 , mounting the fixing member  6  to the shell  4 , specifically to the second annular recessed portion  44 , causes the oil port member  5  to be fixed in a predetermined position to the shell  4 . 
     With the arrangement above, since the outer diameter D 1  of the bellows main body  31  is smaller than the inner diameter d 4  of the opening portion  4   a  of the shell  4  (D 1 &lt;d 4 ; see  FIG. 1 ) and the outer diameter D 3  of the mounting portion  51  of the oil port member  5  is greater than the outer diameter D 1  of the bellows main body  31  (D 1 &lt;D 3 ; see  FIG. 1 ), when the bellows main body  31  welded and fixed to the oil port member  5  is inserted through the opening portion  4   a  of the shell  4  and the oil port member  5  is fixed detachably to the shell  4  with the fixing member  6 , the bellows main body  31  and the oil port member  5  can be mounted to the shell  4 , and further the bellows main body  31  and the oil port member  5  can be drawn and detached together through the opening portion  4   a  of the shell  4  for easier maintenance of the bellows main body  31 . In addition, the annular seal portion S 2  is formed by the O-ring  52  interposed between the outer peripheral surface  51   a  of the mounting portion  51  of the oil port member  5  and the first annular recessed portion  43  of the shell  4 , which can prevent liquid within the liquid chamber  8  of the housing  2  from leaking out. 
     Specifically, as in the related art, for example, in the case of a metal bellows-type accumulator  1  in which the outer peripheral surface  51   a  of the mounting portion  51  of the oil port member  5  is welded and fixed to the second annular recessed portion  44  formed in the cylindrical portion  42  of the shell  4  to seal the opening portion  4   a  of the shell  4 , it is necessary to precisely weld the shell  4  and the oil port member  5  in the circumferential direction to ensure a sealing performance of the housing  2 . In this case, the shell  4  and the oil port member  5  are welded and therefore cannot be separated, which makes it difficult to perform the operation of maintenance such as replacement of the bellows main body  31 . 
     On the other hand, the first embodiment of the accumulator  1  according to the present invention is configured such that the annular seal portion  92  is formed by the O-ring  52  interposed between the outer peripheral surface  51   a  of the mounting portion  51  of the oil port member  5  and the first annular recessed portion  43  of the shell  4 , which can prevent liquid within the liquid chamber  8  of the housing  2  from leaking out, whereby the housing  2  can have a high sealing performance without welding the shell  4  and the oil port member  5 . Moreover, since the male screw portion  61   b  formed on the mounting portion  61  of the fixing member  6  is screwed into the female threaded portion  44   b  of the second annular recessed portion  44  of the shell  4  as described above, it is possible to maintain the state where the opening portion  4   a  of the shell  4  is sealed by the oil port member  5  and thereby to fix the oil port member  5  to the shell  4  with the separate fixing member  6  that is easily attachable and detachable to/from the shell  4 , whereby the operation of fixation/separation of the oil port member  5  to/from the shell  4  can be simplified for easier maintenance of the bellows main body  31 . 
     Also, since the fixation of the oil port member  5  to the shell  4  is achieved through screw-fixation of the fixing member  6 , which is separate from the oil port member  5 , the oil port member  5  cannot be rotated together with the fixing member  6  during screw-fixation of the fixing member  6  to the shell  4 , whereby it is possible to prevent the O-ring  52  from being rubbed and therefore abraded between the outer peripheral surface  51   a  of the mounting portion  51  of the oil port member  5  and the first annular recessed portion  43  of the shell  4 . 
     Further, since the fixation of the oil port member  5  with the bellows main body  31  welded and fixed thereto to the shell  4  is achieved not through welding but through screw-fixation, the oil port member  5  cannot be thermally deformed during fixation to the shell  4  and the residual stress on the oil port member  5  after the fixation can be reduced. 
     Also, when the bellows main body  31  and the oil port member  5  are detached from the opening portion  4   a  of the shell  4 , the gas plug  41  in the gas enclosure port  40  of the shell  4  is first loosened so that the high-pressure gas within the gas chamber  7  is discharged and thereby the gas pressure within the gas chamber  7  is reduced. In this state, the bellows main body  31  is applied with no stress from the high-pressure gas and can be detached safely. Further, the gas enclosure port  40  can enclose high-pressure gas injected in the gas chamber  7  through follow-up screw-fixation of the gas plug  41  for easier maintenance of the accumulator  1 . 
     Also, since the movement of the oil port member  5  in the axial direction (i.e. the direction of insertion) can be restricted by bringing the interior surface (i.e. the upper surface) in the outer peripheral portion of the mounting portion  51  of the oil port member  5  into contact with the first annular stepped portion  45  formed in the cylindrical portion  42  of the shell  4 , the oil port member  5  can be positioned easily with respect to the shell  4 . 
     Also, through screw-fixation of the fixing member  6  to the shell  4 , the outer peripheral portion of the mounting portion  51  of the oil port member  5  can be fixed in a manner sandwiched between the first annular stepped portion  45  of the shell  4  and the annular convex portion  62  of the fixing member  6 , whereby the oil port member  5  can be prevented from being rotated with respect to the shell  4 . Further, through screw-fixation of the fixing member  6  to the shell  4 , an axially pressing stress (toward the first annular stepped portion  45 ) can act on the outer peripheral portion of the mounting portion  51  of the oil port member  5 , whereby the oil port member  5  can be prevented from being rotated with respect to the shell  4  during use of the accumulator  1 . 
     Also, since the fixing member  6  has an annular configuration, through screw-fixation of the fixing member  6  to the shell  4 , an axially pressing stress can act evenly on the outer peripheral portion of the mounting portion  51  of the oil port member  5 . The total weight can also be reduced compared to a disk-shaped configuration. 
     Also, in the inner peripheral surface  42   a  of the cylindrical portion  42  of the shell  4 , the second annular stepped portion  46  is formed between the first annular recessed portion  43  and the second annular recessed portion  44 , whereby the axial position of the annular convex portion  62  of the fixing member  6 , which is formed to have an outside diameter D 3  approximately equal to the inside diameter d 3  of the first annular recessed portion  43 , cannot be restricted and therefore the oil port member  5  can be fixed reliably in an adequate axial position to the shell  4 . 
     In addition, the male screw portion  61   b  formed on the outer peripheral surface  61   a  of the mounting portion  61  of the fixing member  6  is screwed into the female threaded portion  44   b  formed in the second annular recessed portion  44  of the inner peripheral surface  42   a  of the cylindrical portion  42  of the shell  4 , which allows the fixing member  6  to be arranged on the radially inside of the shell  4 , whereby the structure of fixation of the oil port member  5  to the shell  4  can be compacted. 
     It is noted that the oil port member  5  may be key-fitted into the shell  4  (e.g. a recessed portion serving as an axially extending key groove is provided in the first annular stepped portion  45  of the shell  4 , into which a projection is fitted serving as an axially extending key on the outer peripheral portion of the oil port member  5 ). In this case, since the key-fitting restricts the relative rotation of the oil port member  5  to the shell  4 , the oil port member  5  is rotated together during screw-fixation of the fixing member  6  to the shell  4 , which can prevent the O-ring  52  from being rotated to ensure a sealing performance. 
     Second Embodiment 
     The second embodiment of the accumulator according to the present invention will next be described with reference to  FIG. 4 . It is noted that components identical to those shown in the above-described embodiment are designated by the same reference signs to omit the redundant description thereof. 
     As shown in  FIG. 4 , the accumulator  101  of the second embodiment is arranged such that a male screw portion  142   c  is formed closer to the opening portion  104   a  of the outer peripheral surface  142   b  of the cylindrical portion  142  of the shell  104 . An O-ring  147  composed of a rubber elastic body is mounted in an annular groove portion  142   d  formed in the outer peripheral surface  142   b  of the cylindrical portion  142  of the shell  104  and recessed radially inward. 
     The oil port member  105  is provided with a fluid outflow and inflow path  150  penetrating in the axial direction. 
     With the arrangement above, the accumulator  101  can be connected detachably to a chassis provided with pressure piping not shown by threading the male screw portion  142   c  on the shell  104  into a female threaded portion formed in the chassis. Also, the O-ring  147  can be interposed between the chassis and the outer peripheral surface  142   b  of the cylindrical portion  142  of shell  104  to connect the accumulator  101  to the chassis in a tightly closed manner. Further, in the state where the accumulator  101  is connected to the chassis in a tightly closed manner, liquid within the pressure piping can flow out of and into the housing  2  through the through hole  60  in the fixing member  6  and the fluid outflow and inflow path  150  in the oil port member  105 . 
     Third Embodiment 
     The third embodiment of the accumulator according to the present invention will next be described with reference to  FIG. 5 . It is noted that components identical to those shown in the above-described embodiments are designated by the same reference signs to omit the redundant description thereof. 
     As shown in  FIG. 5 , the accumulator  201  of the second embodiment is arranged such that an annular convex portion  261  is provided protruding from the outer surface (lower surface) of the mounting portion  251  of the oil port member  205  toward the opening portion  204   a  of the shell  204 . The annular convex portion  261  is formed to have an outer diameter approximately equal to the inner diameter of the second annular recessed portion  244  formed in the cylindrical portion  242  of the shell  204 , on the outer peripheral surface  261   a  of which a male screw portion  261   b  is formed. That is, the oil port member  5  and the fixing member  6  in the above-mentioned first embodiment are formed integrally. 
     With the arrangement above, the accumulator  201  can maintain the state where the opening portion  204   a  of the shell  204  is sealed by the oil port member  205  by screwing the male screw portion  261   b  formed on the annular convex portion  261  of the oil port member  205  into the female threaded portion  244   a  formed in the second annular recessed portion  244  of the shell  204 , which requires no additional fixing member to fix the oil port member  205  to the shell  204 , whereby the operation of fixation/separation of the oil port member  205  to/from the shell  204  can be simplified for easier maintenance of the bellows main body  31 . 
     Fourth Embodiment 
     The forth embodiment of the accumulator according to the present invention will next be described with reference to  FIG. 6 . It is noted that components identical to those shown in the above-described embodiments are designated by the same reference signs to omit the redundant description thereof. 
     As shown in  FIG. 6 , the accumulator  301  of the fourth embodiment is arranged such that a female threaded portion  342   c  is formed closer to the opening portion  304   a  of the outer peripheral surface  342   b  of the cylindrical portion  342  of the shell  304 . 
     The fixing member  306  has an upward opened cup shape with the mounting portion  361  extending out to cover the opening portion  304   a  of the shell  304  on the radially outside, and is provided with a through hole  360  penetrating axially on the radially inside to have an annular shape. Also, the mounting portion  361  is formed to have an inner diameter approximately equal to the outer diameter of the female threaded portion  342   c  formed in the outer peripheral surface  342   b  of the cylindrical portion  342  of the shell  304 , and a male screw portion  361   b  is formed on the inner peripheral surface  361   a  of the mounting portion  361 . 
     The upper surface of the fixing member  306  is also formed with an annular convex portion  362  protruding upward (toward the oil port member  5 ) from the mounting portion  361  and having an outer diameter approximately equal to the inner diameter of the first annular recessed portion  343  formed in the cylindrical portion  342  of the shell  304 . 
     With the arrangement above, the accumulator  301  can maintain the state where the opening portion  304   a  of the shell  304  is sealed by the oil port member  5  by screwing the male screw portion  361   b  formed on the inner peripheral surface  361   a  of the mounting portion  361  of the fixing member  306  into the female threaded portion  342   c  formed in the outer peripheral surface  342   b  of the cylindrical portion  342  of the shell  304 , and it is also possible to fix the oil port member  5  to the shell  304  with the separate fixing member  306  that is easily attachable and detachable to/from the shell  304 , whereby the operation of fixation/separation of the oil port member  5  to/from the shell  304  can be simplified for easier maintenance of the bellows main body  31 . 
     In addition, since the outer peripheral portion of the mounting portion  51  of the oil port member  5  can be fixed in a manner sandwiched between the first annular stepped portion  345  of the shell  304  and the annular convex portion  362  of the fixing member  306 , whereby the oil port member  5  can be fixed in a predetermined position to the shell  304  and prevented from being rotated with respect to the shell  304 . 
     Fifth Embodiment 
     The fifth embodiment of the accumulator according to the present invention will next be described with reference to  FIG. 7 . It is noted that components identical to those shown in the above-described embodiments are designated by the same reference signs to omit the redundant description thereof. 
     As shown in  FIG. 7 , the accumulator  401  of the fifth embodiment is arranged such that an annular groove portion  444   a  recessed radially outward is formed in the second annular recessed portion  444  of the cylindrical portion  442  of the shell  404 . 
     The oil port member  405  is provided with a protrusion  461  protruding from the outer surface (i.e. the lower surface) of the mounting portion  451  toward the opening portion  404   a  of the shell  404 . The protrusion  461  is formed to have an outer diameter approximately equal to the inner diameter of the second annular recessed portion  444  formed in the cylindrical portion  442  of the shell  404  and also to be fitted into the second annular recessed portion  444  in the state where the interior surface (i.e. the upper surface) is in contact with the second annular stepped portion  446  formed in the cylindrical portion  442  of the shell  404 . 
     The fixing member  406  has an approximately C-shaped stop ring form and is formed to have an outer diameter greater than the inner diameter of the second annular recessed portion  444  formed in the shell  404  and approximately equal to the inner diameter of the groove portion  444   a  formed in the second annular recessed portion  444  of the shell  404 . It is noted that the fixing member  406  is not limited to have an approximately C shape as long as having a stop ring form. 
     With the arrangement above, the accumulator  401  can maintain the state where the opening portion  404   a  of the shell  404  is sealed by the oil port member  405  by fitting the fixing member  406  of a stop ring form into the groove portion  444   a  formed in the second annular recessed portion  444  of the shell  404 , and it is also possible to fix the oil port member  405  to the shell  404  with the separate fixing member  406  that is easily attachable and detachable to/from the shell  404 , whereby the operation of fixation/separation of the oil port member  405  to/from the shell  404  can be simplified for easier maintenance of the bellows main body  31 . 
     In addition, since the outer peripheral portion of the protrusion  461  of the oil port member  405  can be fixed in a manner sandwiched between the second annular stepped portion  446  of the shell  404  and the fixing member  406 , whereby the oil port member  405  can be fixed in a predetermined position to the shell  404  and prevented from being rotated with respect to the shell  404 . 
     While the examples of the present invention have heretofore been described with reference to the accompanying drawings, the specific configuration is not intended to be limited to these embodiments, and modifications and additions within the scope not departing from the spirit of the present invention will also be encompassed by the invention. 
     For example, in the above-described embodiments, the accumulators  1 ,  101 ,  201 ,  301 ,  401  are each described as an outward gas-type accumulator in which the gas chamber  7  is set on the outside of the bellows  3 , while the liquid chamber  8  is set on the inside of the bellows  3  but, without limiting thereto, may be, for example, an inward gas-type accumulator in which the liquid chamber  8  is set on the outside of the bellows  3 , while the gas chamber  7  is set on the inside of the bellows  3  (see  FIG. 8 ). 
     Also, in the above-described embodiments, the housing  2  is described that the opening portion  4   a ,  104   a ,  204   a ,  304   a ,  404   a  of the bottomed cylindrical shell  4 ,  104 ,  204 ,  304 ,  404  is sealed by the oil port member  5 ,  105 ,  405  to be fixed using the fixing member  6 ,  306 ,  406  or the oil port member  205  configured integrally with the fixing member but, without limiting thereto, may be arranged such that opening portions at the upper and lower ends of a cylindrical shell opened at the both ends are sealed, respectively, by an oil port member to be fixed using fixing means and a gas enclosure member. 
     Although the embodiments have been described as an aspect in which the O-ring  52  is mounted in the groove portion  51   b  formed in the oil port member  5 ,  105 ,  205 ,  405 , the O-ring may be mounted in a groove portion formed in the inner peripheral surface of the cylindrical portion of the shell. Further, the O-ring is not limited to be interposed between the outer peripheral surface of the mounting portion of the oil port member and the first annular recessed portion of the shell, but may be arranged freely as long as capable of ensuring a sealing performance between the shell and the oil port member. For example, the O-ring may be mounted in the fixing member. 
     Moreover, the annular seal member is not limited to an O-ring, but may be a seal member of another type such as packing. 
     REFERENCE SIGNS LIST 
       1  Accumulator 
       2  Housing 
       3  Bellows 
       4  Shell 
       4   a  Opening portion 
       5  Oil port member (base body) 
       6  Fixing member 
       7  Gas chamber 
       8  Liquid chamber 
       31  Bellows main body 
       31   a  Fixed end (one end portion of the bellows) 
       42  Cylindrical portion 
       42   a  Inner peripheral surface 
       43  First annular recessed portion 
       43   a  Inner peripheral surface 
       44  Second annular recessed portion 
       44   a  Inner peripheral surface 
       44   b  Female threaded portion 
       45  First annular stepped portion (restrictive stepped portion) 
       46  Second annular stepped portion 
       50  Fluid outflow and inflow path (through hole) 
       51  Mounting portion 
       51   a  Outer peripheral surface 
       51   b  Groove portion 
       52  O-ring (annular seal member) 
       54  Second annular convex portion 
       54   a  Welded portion 
       61  Mounting portion 
       61   a  Outer peripheral surface 
       61   b  Male screw portion 
       62  Annular convex portion 
     S 1 , S 2  Seal portion