Patent Publication Number: US-10330124-B2

Title: Accumulator device

Description:
FIELD OF THE INVENTION 
     The invention relates to an accumulator device, in particular in the form of a piston accumulator, having a floating piston. The piston is inside an accumulator housing and separates two media chambers from each other. In particular, it separates a chamber containing a working gas, such as nitrogen, from a chamber containing a working fluid, such as hydraulic oil. 
     BACKGROUND OF THE INVENTION 
     Accumulator devices of this type are known in a variety of sizes and embodiments and are available on the market. They are widely used in hydraulic systems of various kinds, for example for storing hydraulic energy, for damping or smoothing pressure fluctuations, and the like. Frequently accumulator devices in the form of piston accumulators are also used in hydraulic systems in working equipment having hydraulic drive units, for instance mobile machines, such as excavators, forklifts, loaders or mobile cranes. 
     Due to the varied and numerous applications, accumulator devices are to be produced in large quantities. The amount of manufacturing costs constitutes an economically extremely important factor. 
     SUMMARY OF THE INVENTION 
     The invention addresses the problem of providing an accumulator device of the aforementioned type, which can be produced particularly efficiently and cost-effectively and which, moreover, is characterized by a particularly favorable operational behavior. 
     According to the invention, this problem is basically solved by an accumulator device having, as one essential feature of the invention, a floating piston that is longitudinally movably guided in a guide. The guide is arranged inside the accumulator housing and extends at least partially along the longitudinal axis of the housing. Because, according to the invention, a guide is provided for the floating piston within the accumulator housing, the accumulator housing can be produced efficiently and at low cost. No expensive internal machining is required for a direct guiding of the floating piston on the inner wall of the housing. 
     A particular advantage of the invention is that an identical unit of a guide and the associated floating piston can be used for varying accumulator housing sizes. A modular design can then be realized for the production of accumulator devices having varying dimensions, resulting in a particularly efficient production at low cost. The presence of a guide extending in the longitudinal direction of the accumulator housing further improves the performance by homogenizing the working gas due to reduced turbulence occurring during operation. 
     The longitudinal extension of the guide may be sized such that the floating piston remains in the guide in every possible movement position thereof. 
     In a particularly advantageous manner, the guide can be formed of a hollow cylinder, preferably having uniform wall thickness, whose free end is fixed on the inside of the accumulator housing. A corresponding hollow cylinder, at whose wall there is no pressure gradient due to the movability of the floating piston in operation, can be produced relatively inexpensively because of the thin walls and can be attached to the inside of the housing by a weld. 
     The guide may be advantageously incorporated into the housing, in such a manner that the floating piston uses parts of the guide and the parts of the accumulator housing, at which one end of the hollow cylinder has been fastened in an impermeable manner, to delimit the media chamber holding the working fluid. 
     In doing so, the parts of the accumulator housing can be part of an upper housing part, in particular in the form of a cover, which follows on its inside at least in part the free frontal outer contour of the floating piston, which contour faces the upper housing part. If the working fluid is not pressurized, this results in a reliable, full-surface contact of the floating piston at the housing wall. 
     For this purpose, the frontal outer contour of the floating piston can be convex in order to rest against the concave inside of the upper housing part as soon as the floating piston has reached one of its end positions. The working fluid is then completely displaced from the assignable media chamber. 
     Advantageously, the accumulator housing and the guide is arranged largely concentrically to each other. The outer side of the guide maintains, at least over a central part of the accumulator housing, a constant distance from the inside of the accumulator housing. 
     The arrangement can advantageously be made in such a manner that the free end of the guide leads into the direction of a bottom part of the accumulator housing. The bottom part is designed as a hemisphere and is preferably an integral part of the cup-shaped lower part of the housing. 
     The longitudinal extension of the hollow cylinder forming the guide can be designed particularly advantageously such that the free end of the guide terminates in a transition area in which the cylindrically shaped central part of the accumulator housing merges into the hemispherical bottom part of the housing. 
     The accumulator housing may be formed particularly advantageously with a weld joint between the upper housing part and with the adjoining housing part covered by the guide while maintaining a predetermined radial distance. The guide then forms a protective cover of the weld during welding. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure: 
         FIG. 1  is a side view of an exemplary embodiment of an accumulator device according to the invention; and 
         FIG. 2  is a side view in section along the line II-II of the accumulator device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The exemplary embodiment depicted in the figures has an accumulator housing  2  having a circular-cylindrical main housing part  6 , an upper housing part  4  and a bottom part  8 . The main housing part  6  and the bottom part  8  form a cup, which is closed except for a gas-filling connector  12  located coaxially to the longitudinal axis  10  of the accumulator. The main housing part  6  and the bottom part  8  are integrally formed, for instance in the form of a deep-drawn part made of a metallic material. The bottom part  8  has the shape of a hemisphere, which merges into a transition region  14  in the cylindrical main housing part  6 . The upper housing part  4  has the shape of a shell with a concavely shaped inside surface  16  and is connected by a weld  18  to the cylindrical main housing part  6  as a fastener of the housing  2 . A fluid port  20  is provided concentrically to the longitudinal axis  10  on the upper housing part  4  for an working fluid concerned, such as hydraulic oil. 
     Although the accumulator device forms a piston accumulator, the accumulator housing  2  is designed in the manner of a housing for a bladder accumulator, i.e. the surface of the inside of the housing  2  is not machined, as is required for conventional piston-type accumulators to form a sliding and guiding surface for the respective floating piston. In a simple and inexpensive manner, as in the invention, this machining function is taken over or replaced by a guide for the floating piston  22 . The guide has a hollow cylinder  24 , which extends in the housing  2  concentrically to the axis  10 . The guide inside surface forms the guide track for the floating piston  22 . One end of the hollow cylinder  24  is impermeably fixed to the upper housing part  4  by welding. Its opposite free end extends into the transition area  14 , where the cylindrical main housing part  6  merges into the bottom part  8 . As the upper end of the hollow cylinder  24  is impermeably closed by the upper housing part  4 , the space above the floating piston  22  located in the hollow cylinder  24  forms the fluid side, separated from the gas side  28 , which is located in the remaining part of the hollow cylinder  24  and outside its open aperture in the remaining housing area, adjacent to the bottom part  8 , by the floating piston  22 . As can be seen in  FIG. 2 , the floating piston  22  has the shape of a cup, the depth of which is determined by the axial extension of a piston skirt  30 , which extends downwards from the cup bottom  32 , overhead in  FIG. 2 . The axial length of the piston skirt  30  is dimensioned such that at the end position of the traversing position occupied by the floating piston  22  in the absence of pressurized working gas, [the cup] contacts the bottom part  8  with its piston skirt  30 . For this axial length of the hollow cylinder  24 , whose open end extends at least into the transition area  14  between the bottom part  8  and the main part  6 , the floating piston  22  therefore remains at the lower end position in guiding engagement with the hollow cylinder  24 . 
     As can be seen, the upper surface of the cup bottom  32  of the floating piston  22  is convexly curved. The curvature is adapted to the concave curvature of the inside  16  of the upper housing part  4  in such a manner that the floating piston  22  in its upper end position, i.e. in the absence of fluid pressure, contacts the inside  16  over the complete surface. Thus, at this end position, the accumulator body  2  is free of any residual volume of remaining liquid. 
     In operation, the floating piston  22  in the hollow cylinder takes a position corresponding to the pressure balance between the fluid side  26  and gas side  28 . No differential pressure is effective on the wall of the hollow cylinder  24 , i.e. the hollow cylinder  24  can be formed as a thin-walled tube using very little material. The assembly of a hollow cylinder  24  and a floating piston  22  can be used as a prefabricated module or block for varying accumulator designs. Optionally, for the same tube diameter and identically constructed floating piston  22 , varying pipe lengths can be provided for different lengths of the accumulator housing. In this way, the invention allows for a cheap construction of accumulator devices in the form of piston accumulators. 
     While one embodiment has 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 claims.