Abstract:
Pressure vessel which is filled with at least one medium which is pre-stressed by a mass of gas enclosed in a deformable enveloping body, in particular for the volume equalization in a vibration damper, comprising a wall in which a pressurized gas is enclosed. The wall is at least partially formed from a gas-tight barrier layer and the enveloping body has sections which are aligned at an angle to one another in the circumferential direction, the wall having an impressed transition between the sections, which are aligned at an angle to one another. The wall may additionally be designed with an expansion profile.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a pressure vessel containing a fluid medium which is pre-stressed by a mass of gas enclosed in a deformable enveloping body.  
           [0003]    2. Description of the Related Art  
           [0004]    Enclosed masses of gas are used, inter alia, wherever a medium is to be put, and retained, under pressure but must not be mixed with an open pressure fluid. They are commonly used in piston/cylinder assemblies such as vibration dampers. Such a vibration damper with an enclosed mass of gas is known, for example, from U.S. Pat. No. 3,294,391, wherein the gas is enclosed in a closed cell polyurethane form. The enclosed mass of gas serves for compensating for the volume of the piston and/or of the piston rod penetrating into the vibration damper. A problem is that gas diffuses through the foam into the damping medium.  
           [0005]    U.S. Pat. No. 6,116,585 describes a pressure vessel with a deformable enveloping body in which a mass of gas is enclosed by an impermeable wall. Tests have shown that, at certain locations, the enveloping body has stress peaks which adversely affect the service life of the pressure vessel. In the case of a rectangular pressure vessel which is fitted into a round installation position, for example in a vibration damper, random inflections may be produced. A measure taken in order to avoid these inflections, as can be seen from FIGS. 2 and 4, has been to provide connections  27 V and thus to achieve sections which run at an angle in the circumferential direction. The above-mentioned stress peaks occurred thereafter.  
           [0006]    A further possibility is to use a round pressure vessel, for example as is illustrated in FIG. 5 of U.S. Pat. No. 6,116,585. The disadvantage with this design is that, for each diameter size of the tube enclosing the pressure vessel, it would be necessary to produce a separate pressure-vessel design if the aim is to use the largest possible pressure vessel and/or if one is seeking optimum utilization of space.  
         SUMMARY OF THE INVENTION  
         [0007]    The object of the present invention is to achieve a pressure vessel, for an enclosed mass of gas, of which the enveloping body has the smallest possible stress peaks.  
           [0008]    According to the invention, the enveloping body is formed by inner and outer walls which are provided with impressed transitions between the sections. The inner and outer walls are not connected at the transitions.  
           [0009]    The impressed transition prevents the enveloping body from being exposed to undefined inflections and also prevents excessive friction from occurring on the walls. Correspondingly rounded transitions minimize the stress states in the enveloping body, with the result that the service life of the enveloping body can be extended to a decisive extent. In a further advantageous configuration, the impressed transition is designed as a radius.  
           [0010]    A further measure according to the invention for minimizing the stress states in the enveloping body consists in the wall being designed with an expansion profile. It is precisely when the wall has a material with a very low level of expansion, e.g. a metal foil, that the expansion of the enveloping body can be achieved by an expansion profile. An expansion profile is to be understood as all folds in the wall which allow a change in length by the fold being straightened out.  
           [0011]    The practical configuration of the expansion profile also has to be considered from an economic point of view. A compromise will be sought between production outlay and expansion capacity of the expansion profile. Extensive tests have shown that an expansion profile with a sinusoidal cross section is particularly well suited since, in this case, only extremely small additional stresses are introduced into the foil/sheet material.  
           [0012]    It may also be advantageous for the impressed transition between the sections, which are aligned at an angle to one another, and the expansion profile to form a superposed profile. Superposed profile is to be understood in the manner that, for example, rather than interrupting the expansion profile, the impressed formation between the sections, which are aligned at an angle to one another, also contains the expansion profile.  
           [0013]    In terms of short cycle times during the production of the pressure vessel, provision may be made for the expansion profile to be restricted to a strip in the region of the impressed transition.  
           [0014]    In order to achieve the best possible action of the expansion profile, the latter extends transversely to the longitudinal axis of the enveloping body. In the case of pressure vessels which are subjected to particularly high loading, provision may also be made for the expansion profile to comprise a plurality of individual expansion profiles.  
           [0015]    For reasons of strength, provision is made for the expansion profile comprising a plurality of individual expansion profiles to bound lozenge-shaped wall segments. It has proven advantageous here if the expansion profiles run obliquely in relation to the longitudinal axis of the pressure vessel and the resulting corner points of the lozenge-shaped wall segments are located on a pitch circle and on lines parallel to the longitudinal axis.  
           [0016]    Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 shows a use example of the enclosed mass of gas in a vibration damper,  
         [0018]    [0018]FIG. 2 shows a section perpendicular to the axis of the vibration damper and the enclosed mass of gas, taken along the plane  2 - 2  of FIG. 1,  
         [0019]    [0019]FIGS. 3 a ,  3   b  show a section through the wall of the enveloping body,  
         [0020]    [0020]FIG. 4 shows a section view of the enveloping body taken along axial plane  4 - 4  of FIG. 2,  
         [0021]    [0021]FIG. 5 shows a plane view of the enveloping body, and  
         [0022]    [0022]FIG. 6 shows an illustration in detail form of the enveloping body.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 1 shows a vibration damper  1  known per se of double-tube design in which a piston rod  3  with a piston  5  is guided such that it can be moved axially in a pressure tube  7 . The piston  5  separates the pressure tube into a top working chamber  9  and a bottom working chamber  11 , the two working chambers being connected via damping valves  13  in the piston.  
         [0024]    The pressure tube  7  is encased by a vessel tube  15 , the inner wall of the vessel tube and the outer wall of the pressure tube forming an equalization chamber  17  which is completely filled with damping medium and an enclosed mass of gas  19  up to a piston-rod guide  21 . Arranged at the bottom end of the working chamber  11  is a base which has, if appropriate, a check valve  23  and a damping valve  25 .  
         [0025]    In the case of a piston-rod movement, the disclosed piston-rod volume is equalized by a change in volume of the enclosed mass of gas.  
         [0026]    [0026]FIG. 2 shows a section through the vibration damper  1  in the region of the enclosed mass of gas  19 . The enclosed mass of gas comprises enveloping body  27  with a wall  29  which is pressure-filled with a gas, in particular nitrogen. It is alternatively possible to use CO 2  or, with correspondingly quick installation, even a liquid gas. The wall  29  has an inner wall  29   i  and an outer wall  29   a , which in turn form a start and an end. In this use example, the enclosed mass of gas is forms an arc in the equalization chamber  17 . In the sectional illustration, it is possible to see sections  41  of the enclosed mass of gas which are arranged in series and are aligned at an angle to one another. The sections  41  are formed by impressed transitions  43  between the inner wall  29   i  and the outer wall  29   a , the transitions running parallel to the axis of the vibration damper.  
         [0027]    The enclosed mass of gas has a filling connection  31  which is accessible via a filling opening  33  in the vessel tube. During the installation of the vibration damper, the non-filled enveloping body is positioned in the vessel tube  15 , the filling connection  31  being fitted into the filling opening. Thereafter, the pressure tube  7  is introduced. The entire vibration damper is then filled with oil, the volume of the oil filling depending on the later operating pressure, which is determined by the enclosed mass of gas when the piston rod is at a standstill. Once the vibration damper has been closed, the enclosed mass of gas can be fed via a filling unit (not illustrated), e.g. injection needle. If the injection needle is removed, the puncture opening closes automatically. Following the filling operation, the filling opening can be closed by a pressed-in ball  35 .  
         [0028]    [0028]FIG. 3 a  illustrates a section through the wall  29 , the inner wall  29   i  and the outer wall  29   a  possibly consisting of the same material and/or being of the same construction. The core of the wall is a metal foil, in particular an aluminum foil  29 Al, which is only a few μm thick. Rolled aluminum is particularly suitable above all. The aluminum foil assumes the sealing function for the enclosed gas. Toward the outside, the aluminum foil is coated by a protective sheet material  29 S. This protective sheet material promotes the stability, increases the tear strength and prevents pronounced creasing. This layer has a thickness in the same range as the aluminum foil and consists, for example, of PET or polyamide.  
         [0029]    Toward the inside, the wall has a weldable coating  29 V. The weldable coating may also be of multi-layered, for example two-layered, design and be of approximately four to five times the material thickness of the aluminum foil. In the case of a multi-layered coating  29 V, the individual layers are drawn out and applied crosswise to one another. This achieves a high strength and dimensional stability, in particular compensation is provided for inner stresses. PP (polypropylene) and PA (polyacrylate) have proven successful materials. The layer thickness is approximately 50 to 100 μm. If PA is used in each case for the protective layer and the weld layer, seal welding can be carried out for the enveloping body. In a seal-welding operation, the protective layer is positioned so as to overlap the weld layer and is welded by heat being supplied.  
         [0030]    [0030]FIG. 3 b  shows the construction of the enveloping body wall additionally having a carrying layer  29 T. The carrying layer ensures the strength in all directions of loading of the enveloping body  29 . When the carrying layer is used, the metal foil  29 Al can be reduced to the absolute minimum. As a result, the enveloping body becomes more flexible and acquires elastomeric properties. Furthermore, the carrying layer constitutes a protection for the metal foil during the welding operation. It has to be ensured that no operating medium from the pressure vessel comes into contact with the metal foil. Depending on the operating medium, the metal foil may be chemically corroded. It is sought for the metal foil  29 Al to be arranged in the neutral fiber of the wall of the enveloping body, in order for the bending stressing to be optimized.  
         [0031]    It is possible to apply between the layers an adhesive-bonding layer  29 K, for example made of PU (polyurethane), which ensures that the layers are held together securely. The adhesive-bonding layer may be applied in the same way as a conventional adhesive or else may be placed in position as an adhesive-bonding sheet material. Alternatively, it is also possible for the individual layers to be calendered.  
         [0032]    [0032]FIG. 4 shows a longitudinal section through a section  41  of the enveloping body  27 . An expansion profile  45  can clearly be seen in this view. The expansion profile is conducive to providing a cushion form of the sections between the impressed transitions  43 . In the region of the transitions  43 , it is possible for the wall to be positioned in folds and to be straightened out to the maximum extent at the equator  47  of the cushion. A sinusoidal expansion profile is illustrated by way of example. A different fold formation is, of course, also conceivable. The sine profile has, for example, a distance from one harmonic wave to the next harmonic wave of 3 mm and an amplitude of between 0.2 and 0.3 mm.  
         [0033]    [0033]FIG. 5 illustrates a projected development of the enveloping body  27 . Weld seams  37  are located on the border, and these produce a closed body from the inner wall  29   i  and the outer wall  29   a . The weldable coating  29 V, see FIG. 3, is required for the weld seams  37 .  
         [0034]    [0034]FIG. 5 shows three possible forms of the configuration of the expansion profile  45 . In the case of the left-hand variant, the expansion profile  45  is restricted to a strip in the region of the impressed transition  43  since it is at this location that the largest stress peaks, which it is intended to minimize, occur. It is also possible for the expansion profile to run parallel to the weld seams  37 , since a larger fold formation is to be expected in this region.  
         [0035]    The central expansion profile  45  is of horizontal design. A horizontal expansion profile can be produced particularly easily. The right-hand variant shows an expansion profile  45  which comprises two cross-crossing individual expansion profiles  45   a ;  45   b , as a result of which lozenge-shaped wall segments  49  are determined. If, as is illustrated, the individual expansion profiles run alternately at 45°, then the points of intersection of the expansion profile are located parallel to the transition sections  43  of the enveloping body  27 . This provides a further lasting improvement to the expansion behavior of the sheath since, with application of force to the points of intersection, the expansion is greater than in the case of a horizontal and vertical design of the expansion profile  45 .  
         [0036]    [0036]FIG. 6 is intended to illustrate that the impressed transition  43  between the sections  41  of the enclosed mass of gas and the expansion profile  45  form a superposed profile in which both profile characteristics are maintained.  
         [0037]    The above-described application for the vibration damper is only to be taken by way of example. Of course, it is also possible to utilize the spring forces of the enclosed mass of gas. Conceivable, for example, is the use as a pneumatic spring, providing partial or full support, as is used, for example, in chassis technology for level control and hydraulic spring elements. In some applications, e.g. in the case of a single-tube damper as a replacement for the equalization chamber, it is necessary to provide a stop which prevents the enveloping body from lifting. The single-tube vibration damper essentially comprises the same components as the vibration damper of double-tube design according to FIG. 1, identical components having the same designations. A possible stop is, for example, a clamped-in ring or, if present, bottom valve  25 .  
         [0038]    Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.