Abstract:
A method produces piston-type accumulators, including an accumulator housing ( 10 ) and a separating piston, which can be displaced in a longitudinal direction inside the accumulator housing ( 10 ) and separates two working spaces located in the housing. One end face of the accumulator housing is sealed by cover part ( 20 ). The cover part ( 20 ) is fixed on one side ( 40 ) via the free longitudinal edge ( 32 ) of the accumulator housing ( 10 ). The edge is displaced towards the cover part ( 20 ), such that a functionally and positionally secure connection of a cover part is ensured within the housing of a piston-type accumulator without using standard threaded connections.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for the production of piston-type accumulators having an accumulator housing and a separating piston displaceable in the longitudinal direction in the accumulator housing and separating two working chambers from each other. The accumulator housing is sealed on each of the end sides by a cover component. 
     BACKGROUND OF THE INVENTION 
     Piston-type accumulators are, in the broadest sense of the term, hydraulic accumulators, which among other things serve the purpose of receiving specific volumes of a pressurized liquid (hydraulic medium) of a hydraulic system and returning these volumes to the system when required. Since the hydraulic medium is pressurized, hydraulic accumulators are treated as pressure reservoirs and must be designed for the maximum excess operating pressure, the acceptance standards of various installing countries being taken into consideration. Hydropneumatic (gas-charged) accumulators with a separating element are currently used in most hydraulic systems. A piston separates a fluid space as working chamber from a gas space as additional working chamber, serving as separating element inside the accumulator housing of the piston-type accumulator. Nitrogen is generally used as the operating gas. The gas-tight piston to a great extent permits disconnection of the gas space from the fluid space. 
     The fluid component is connected to the hydraulic circuit so that, as the pressure rises, the piston-type accumulator admits or receives fluid and the gas is compressed in the process. As the pressure drops, the compressed gas expands and displaces the pressurized fluid back into the hydraulic circuit. One advantage of piston-type accumulators is they can “work” when in any position, but preference is given to vertical positioning with the gas side on top, so that settling of fouling particles from the fluid on the piston seals is prevented. 
     Consequently, the essential components of a piston-type accumulator are an outer cylindrical tube forming the accumulator housing, the piston forming the separating element with its sealing system, and the sealing covers on the housing ends. The cover elements also contain a fluid connection and a gas connection. Two functions are regularly assigned to the accumulator housing, specifically storage of internal pressure and ensuring control of the piston inside the accumulator housing. The cover components on the front surface sealing the interior of the accumulator housing off from the exterior are provided on the outer circumference with external threading which may be screwed into a corresponding inner threading along the free longitudinal edge over an assigned path. Production of the respective threaded connection is time-consuming; and correspondingly increases the production costs of the piston-type accumulator. In addition, safety measures must be taken to secure the cover component in its position. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved manufacturing process for piston-type accumulators where a reliable operation of a cover component secured in position in the accumulator housing is guaranteed, and where the otherwise customary threaded connections are avoided. 
     This object is basically attained by a method or process in which the cover component on one of its sides is fastened by the free longitudinal edge of the accumulator housing, which housing edge is for this purpose moved onto the cover component. The otherwise customary screw connection is avoided for the cover component. A clamping onto the free end of the accumulator housing is achieved in which the cover component is clamped at least over the free longitudinal edge of the accumulator housing after this housing has been moved onto the cover component. It is sufficient if a part of the free longitudinal edge effects this clamping. 
     In one preferred embodiment of the method of the present invention, at least one of the two cover components is inserted until one cover side engages a stop in the interior of the accumulator housing such that the respective cover component is retained in its end position by the clamping force of the longitudinal edge introduced. If a stop is provided on the inside of the accumulator housing, the cover component may be immobilized against this stop during the positioning movement of the free longitudinal edge of the accumulator housing. In addition or as an alternative, however, the possibility exists of inserting the cover component into the free end of the accumulator housing and then initiating the positioning movement of the free end of the accumulator housing. The positioning movement may be effected toward the upper or outer side of the cover if the cover component is retained in a suitable position. An unrestrained positioning movement may also be effected for the longitudinal edge and then, in the state of readiness for operation, the cover component may be moved by the piston against the free longitudinal edge, which then effects the clamping there. 
     Preferably, a shaping tool is provided for the positioning movement of the longitudinal edge of the accumulator housing. The tool is provided with positioning bevels and positions the longitudinal edge of the accumulator housing on the cover component in such a way that this cover component is secured in the accumulator housing as the clamping seat. 
     In one especially preferred embodiment of the method of the present invention, two shaping tools positioned on opposite sides carry out the fastening process for the respective end cover component in a common positioning movement to the accumulator housing. These shaping tools act on the free longitudinal edge of the accumulator housing. It has been found to be highly advantageous for the purpose of generation of high fastening forces to position the two free ends of the cylindrical accumulator housing uniformly. The shaping tool which acts on one end of the accumulator housing is capable in addition of reliably withstanding the forces introduced onto the accumulator housing by the other shaping tool. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIG. 1  is a side elevational view in section of a conventional piston-type accumulator; 
         FIG. 2  is a side elevational view in section of the upper part of a piston-type accumulator with a shaping tool positioned above it, according to a first embodiment of the present invention; 
         FIGS. 3 and 4  are side elevational views in section of the positioning of a positioning tool on the free end of the accumulator housing for the purpose of fastening the respective cover component, according to a second embodiment of the present invention; 
         FIGS. 5 and 6  are side elevational views in section of the upper areas of the accumulator housing in the form of two different versions with insertion bevels positioned in the interior for introduction of the respective cover component, according to third and fourth embodiments of the present invention, respectively; and 
         FIG. 7  is a side elevational view in section of the upper part of a piston-type accumulator housing with modified cover component, according to a fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The conventional piston-type accumulator shown in  FIG. 1  has an accumulator housing  10  in the form of an outer cylindrical tube. A piston  12  with its sealing system  14  on the piston exterior is introduced as separating element so as to be longitudinally displaceable in the housing. Inside the accumulator housing  10 , the piston  12  separates two working chambers  16 ,  18  from each other, one working chamber  16  serving to receive an operating gas, in particular one in the form of nitrogen, while the other working chamber  18  forms the fluid space for the piston-type accumulator. The displaced position of the piston  12  and accordingly the volume percentages of gas and fluid in the working chambers  16  and  18  vary with the operating situation of the accumulator. A cover component  20 ,  22  is mounted on each end of the accumulator housing  10  having a gas connection  24  for recharging with nitrogen operating gas and a fluid connection  26  for connecting the piston-type accumulator to an overall hydraulic system (not shown), respectively. 
     Each of the two cover components  20 ,  22  is provided with external threading  28  which may be engaged with internal threading  30  extending along the free longitudinal edge  32  and outward to the exterior. On the external circumference side, each cover component  20 ,  22  is provided with a seal  34  for sealing the interior of the accumulator housing  10  from the exterior. Application of the lengths of threading  28 ,  30  entails a certain production effort making the prior piston-type accumulators complex and expensive to produce. It is also necessary to secure each cover component  20 ,  22  from rotation to ensure its fixing in position inside the accumulator housing  10 . One possible method of securing the respective cover component  20 ,  22  from rotation involves providing a conventional adhesive seal along the threading  28 ,  30 , or by keeping the cover component in its position by a conventional retention bore (with and without threading). 
     Based on this prior art, the method of the present invention will now be described in greater detail with reference to  FIGS. 2-7 . This solution permits cost-effective creation of a reliably operating connection of cover component and the associated accumulator housing  20 . For the sake of greater simplicity of presentation, only the upper end of the accumulator housing  10  is shown in  FIG. 2 , along with the upper cover component  20 . When reference is made to these structural components below, as with the prior art embodiment shown in  FIG. 1 , the respective structural components are designated by the same reference numbers as in  FIG. 1 . 
     The method of the present invention is among other things characterized in that the respective cover component, in this instance cover component  20 , is inserted by its lower or inner side  36  to come into contact with a stop or shoulder  38  in the form of an annular surface in the interior of the accumulator housing  10 . The cover component is secured on its opposite side  40  by the free longitudinal edge  32  of the accumulator housing  10 . The longitudinal edge  32  undergoes a positioning movement relative to the cover component  20 , as is to be explained in greater detail in what follows. 
     An axially movable shaping tool  42  serves to position the longitudinal edge  32  of the accumulator housing  10 . This shaping tool  42  is provided with at least one positioning bevel  44  which positions the longitudinal edge  32  onto the cover component  10  so that this cover component is secured as a clamping seat in the accumulator housing  10  between the stop  38  and the longitudinal edge  32 . For the purpose of establishing the respective clamping seat, the upper or outer side  40  of the cover component  20  is provided with a circumferential contact surface  46  tapering toward the longitudinal axis  48  of the accumulator housing  10  in the outward direction of the cover component. The inclination of the contact surface  46  corresponds to the inclination of the positioning bevel  44  of the shaping tool  42 . However, other obvious inclinations or bevels are also conceivable. As is shown in  FIG. 2 , the positioning direction for the shaping tool  42  is that of the longitudinal axis  48  of the accumulator housing  10  or of the piston-type accumulator as a whole. 
     For the sake of greater clarity of illustration, the separating element in the form of the piston  12  is omitted from  FIG. 2 , as are the gas connection  24  shown in  FIG. 1 , which is also an integral part of the upper cover component  20 . Before the clamp connection is effected by the shaping tool  42 , the upper free end of the accumulator housing with its upper longitudinal edge  32  has an outline as shown in  FIGS. 3 to 6 . The wall thickness of the longitudinal edge  32  is reduced in comparison to the rest of the accumulator housing  10 . The area of transition between the different wall thicknesses forms the stop  38  for the cover component  20 . In addition, the longitudinal edge  32  is provided with a tapering insertion bevel  50 , by preference on its side facing the cover component  20 . The bevel is oriented outward. The respective insertion bevel  50  facilitates introduction of the cover component  20  into the free upper end of the accumulator housing  10 , as will be described in greater detail below. Cover component  10  is inserted into the housing until its inner surface  36  engages stop  38  to prevent further insertion. 
     As is shown in  FIGS. 4 and 5  in particular, the free longitudinal edge  32  may also be provided on the external circumference side with a slide bevel  52  oriented toward the free end of the accumulator housing  10 . This slide bevel makes it easier for the longitudinal edge  32  to effect transition from its cylindrical shape as shown in  FIGS. 3 to 6  to an inclined position after being positioned. The slide bevel  52  slides along the positioning bevel  44  of the shaping tool  42  until the shaping tool is visibly mounted on the accumulator housing  10  in the direction of positioning. Once the axial positioning movement by the shaping tool  42  has been completed, the longitudinal edge  32  is inclined along the contact surface  46  of the cover component  20  to form a fastening bevel. In this way, the cover component  20  is secured against the stop  38  inside the accumulator housing  10 . 
     To avoid endangering the secure position of the cover component  20  in the accumulator housing  10  and also to protect the cover component  20  from introduction of harmful forces, the free longitudinal edge  32  is, as shown in  FIG. 2 , guided along its free end so as to project over the second side  40  of the cover component  20 . After the clamp connection has been secured, the shaping tool  42  is moved back away from the accumulator housing  10  and then, for example, assumes its upper position as illustrated in  FIG. 2 . By preference the shaping process for the respective longitudinal edge  32  of the accumulator housing  10  is effected as cold forming, but hot forming involving appropriate heating of the accumulator housing material and preferably the shaping tool  42  as well is also conceivable. A conventional easily shaped steel material is used for the accumulator housing  10  with its longitudinal edge  32 . To introduce the clamping forces optimally into the cover component  20  and also to ensure optimal support for the cover component  20  in the accumulator housing  10 , the edge side is made such that the height of the cover component  20  is adapted to the application conditions assigned by operation of the accumulator. In the case illustrated, the cover component  20  is at least twice as great as the length of the longitudinal edge  32  between its free end and a deflection point  54  from which the longitudinal edge  32  is moved onto the top of the cover. 
     Specifically, the method for producing a piston accumulator involves mounting a piston in an accumulator housing  10  for movement along a longitudinal axis  48  of the housing  10  with the piston separating an interior of the housing into two working chambers between first and second longitudinal ends of the housing. A first shoulder  38  in the interior of the housing  10  is provided adjacent to but spaced from the first longitudinal end  32  of the housing  10  to form a first end portion of the housing with a reduced wall thickness relative to an adjacent portion of the housing, with a transition part between different wall thicknesses forming the first shoulder  38 . A first cover component  20  is inserted at least partially within the housing  10  through the first longitudinal end when open until an inner surface portion of the first cover component engages the first shoulder  38  preventing further insertion of the first cover component. The first end portion of the housing is deformed to form a bend  54  between the first shoulder and the first longitudinal end through an acute angle relative to the longitudinal axis against an axially facing outer circumferential contact surface  46  extending at a corresponding acute angle relative to the longitudinal axis and about an axially facing outer surface portion  40  of the first cover component radially within the outer circumferential contact surface to secure the first cover component in the housing with the first cover component sealing the first longitudinal end of the housing closed by moving a first shaping tool  42  only axially along the longitudinal axis, the first shaping tool being unitary without any relatively movable parts. The second longitudinal end of the housing is sealed closed in the same manner. 
     As shown in  FIG. 2 , each end portion of the housing extending directly from the respective longitudinal end is deformed to form an obtuse angle with an axially aligned section of the housing between deflection point or bend  54  and the respective shoulder or stop  38 . 
     As is illustrated in  FIG. 7  for a modified embodiment, the cover component  20  may nevertheless project beyond the longitudinal edge  32  of the accumulator housing  10 , or, in another embodiment not shown, may end so as to be flush at the same level. 
     In one especially preferred embodiment (not shown) of the method of the present invention, the fastening process for the end cover components  20 ,  22  is carried out in a common axial positioning movement of two shaping tools  42  on opposite ends of the accumulator housing  10  simultaneously with more or less equal shaping forces acting on the free longitudinal edges  32  of the accumulator housing  10 . In such shaping method, each shaping tool can, during shaping, receive the forces of the other shaping tool such as occur during the forming process. Costly support devices may be dispensed with in this configuration on the respective opposite sides where the shaping tool  42  exerts no effect. Harmonious introduction of forces into the accumulator housing  10  without the occurrence of damaging power peaks also occur in this situation. 
     As is shown in  FIGS. 3 and 4 , the respective cover component  20 ,  22  may be introduced into the accumulator housing  10  up to the stop  38  in the form of an annular surface by a positioning tool  56 . As shown in  FIG. 4 , positioning tool  56  encloses the free longitudinal edge  32  of the accumulator housing  10 . The positioning tool  56  has for the introduction process, a feed bevel  58  along which the cover component  20  or  22  may slide on its external circumference side. Use of the positioning tool  56  reliably prevents possible damage to the seal  34  of the cover component  20  or  22 . In addition to the feed bevel  58 , the positioning tool  56  has an admission space  60  into which the upper end of the accumulator housing  10  may be introduced so that the feed bevel  58  ends flush with the upper edge of the longitudinal edge, and in addition effects uninterrupted transition to the admission area  62  for the cover component  20 ,  22  in the accumulator housing  10 . 
     In the embodiments shown in  FIGS. 5 and 6 , the accumulator housing  10  is provided on the inner circumference side along its upper longitudinal edge  32  with an insertion bevel  50  extending outwardly in the direction of the length of the accumulator housing  10 . This bevel results in a slip edge over which the respective cover component  20 ,  22  may also be introduced and later secured. This alternative may be selected if the cover seal  34  is rugged and not overly susceptible to damage. 
     The same reference numbers are used for the same structural parts illustrated in  FIG. 7 . The method employed is described only to the extent that it differs significantly from the method described in the foregoing. In the embodiment shown, the upper cover component  20  is retained by the free longitudinal edge  32  of the accumulator housing  10  so that the upper side projects a predetermined distance beyond the end of the free longitudinal edge  32 . In the embodiment shown in  FIG. 7 , the stop  38  for the cover component  20  is provided with a bevel against which the cover component  20  leans in a stepped recess. The annular seal  34  is in turn received in the outer circumference of the recessed sectional step  64 . Because of the stepped arrangement illustrated for accumulator housing  10  and cover component  20 , the possibility exists of machining the accumulator housing  10  as finely as possible for clean contact with the sealing ring  34  at this point and of leaving the inside of the accumulator housing  10  more or less unmachined, insofar as the delivery area for the free longitudinal edges  32  of the accumulator housing  10  is affected. 
     The cover components  20 ,  22  may accordingly be fastened with high fitting accuracy, reliably, and pressure-tightly in the accumulator housings  10  by the shaping process discussed, in the widest possible variety of embodiments. Screw connections that are cost-intensive in mounting, in addition remain to be secured in this position, and may be dispensed with in their entirety. 
     While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.