Abstract:
A pressure fluid accumulator with a housing having its interior subdivided by a media-separating element into two chambers, the first chamber being filled with a gas and the second chamber being filled with a liquid, and wherein in a hydraulic port a bottom valve is provided which permits filling the second chamber with liquid and prevents complete evacuation of the second chamber, and the valve&#39;s closure member is operable by the media-separating element. In order to prevent, especially at low temperatures and high viscosity of the pressure fluid, damage of the media-separating element caused by a high differential pressure, a device is provided between the media-separating element and the bottom valve.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to pressure fluid accumulators and more particularly relates to a pressure fluid accumulator with a housing having its interior subdivided by a media-separating element into two chambers, the first chamber being filled with a gas and the second chamber being filled with a liquid.  
         BACKGROUND OF THE INVENTION  
         [0002]    A pressure fluid accumulator of this type is disclosed in international patent application WO 00/31420. The bottom valve of the prior-art pressure fluid accumulator is composed of an elastic sealing element, which upon closing cooperates with a conical annular surface designed in the bore of the hydraulic port. The closing operation takes place in two phases. In the first phase, in which the pressurized pressure fluid flows past the sealing element, the closure member of the bottom valve is pushed so far downwards by the media-separating element until the sealing element comes into contact with the conical annular surface and prevents the exit of the pressure fluid out of the second chamber. In the subsequent second closing phase, the closure member fulfils the function of a hydraulic piston that is displaced further in a downward direction due to the residual pressure acting in the second chamber.  
           [0003]    When the pressure fluid cools down after closure of the bottom valve, the media-separating element will move further downwards in the direction of the bottom valve. If, however, it comes to a rest in the direct vicinity of the closure member of the bottom valve, it is not possible to completely open the bottom valve in the subsequent filling operation so that the fluid must pass over the sealing element fitted to the closure member. Because the slot bounded by the wall of a bore that accommodates the closure member and by the sealing element is very small, a high differential pressure is necessary for the filling operation, in particular at low temperatures and high viscosity of the pressure fluid. Consequently, a high amount of hydraulic force acts on the closure member, urging the closure member against the bottom of the media-separating element. This produces a relatively great pressure difference, up to 10 bar, between the two chambers, with the imminent risk of damage of the media-separating element. Due to this drawback, in many instances, it is not possible for the prior-art pressure fluid accumulator to reach their useful life.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    In view of the above, an object of the present invention is to improve upon a pressure fluid accumulator of the above-mentioned type to such effect that damage of the media-separating element during the filling operation is prevented to the greatest extent possible and, thus, a considerable increase in the operational safety is safeguarded.  
           [0005]    According to the present invention, this object is achieved in that a means for reducing the force that can be transmitted from the closure member of the bottom valve to the media-separating element is provided between the media-separating element and the bottom valve.  
           [0006]    To render the idea of the present invention more precise, the means is configured as a spring, preferably a compression spring being supported on the closure member of the bottom valve and movable into abutment on the media-separating element.  
           [0007]    In a favorable aspect of the object of the invention, the compression spring abuts on the media-separating element by means of a force-transmitting member that is slidably guided in the closure member. In this arrangement, the closure member is preferably preloaded in opposition to the closing direction by means of a valve spring whose spring rate is lower than the spring rate of the compression spring.  
           [0008]    Further favorable features of the present invention are stated in sub claims  4  to  18 . 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is an axial cross-sectional view of an embodiment of the pressure fluid accumulator of the invention with the bottom valve closed.  
         [0010]    [0010]FIG. 2 is an enlarged view of the bottom valve of the pressure fluid accumulator in its open condition according to FIG. 1.  
         [0011]    [0011]FIG. 3 is an enlarged view of a second embodiment of the bottom valve in its open condition.  
         [0012]    [0012]FIGS. 4 a,b  is a view of a third embodiment of the bottom valve in its open and closed conditions.  
         [0013]    [0013]FIG. 5 a,b  is a fourth to seventh embodiment of the  
         [0014]    through  8   a,b  bottom valve in its open and closed conditions.  
         [0015]    [0015]FIGS. 9 a - d  show phases of operation of an eighth embodiment of the bottom valve of the invention.  
         [0016]    [0016]FIGS. 10 a - d  show the phases of operation according to FIGS. 9 a - d  in a ninth embodiment of the bottom valve of the invention.  
         [0017]    [0017]FIGS. 11 a,b  show a tenth embodiment of the bottom valve in its open and closed conditions.  
         [0018]    [0018]FIGS. 12 a,b  show an eleventh embodiment of the bottom valve in its open and closed conditions. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The pressure fluid accumulator of the present invention as illustrated in FIG. 1 has a housing  1 , with its interior subdivided into two pressure compartments or chambers  3 ,  4  by means of a media-separating element  2 . The media-separating element  2  is preferably formed by a thin-walled metallic pleated bellows, which is connected pressure-tightly to a cover  9  that closes the housing  1 , on the one hand, and is closed by a plate  8 , on the other hand. The interior of the pleated bellows  2  houses the first chamber  3 , which can be filled with a gas that is generally under high pressure by way of a fill port  29  provided in the cover  9 . In the bottom part of the housing  1 , a hydraulic port  5  is provided in which a bottom valve  6  is arranged whose closure member  7  projects into the second chamber  4  in the open position of the bottom valve (FIG. 2). The bottom valve  6  is preferably configured so that it permits filling the second chamber  4  with a pressurized fluid, such as a brake fluid, on the one hand, and prevents complete evacuation of the second chamber  4 , on the other hand. To achieve centering of the pleated bellows  2  in the housing  1 , there is provision of a slotted ring  30  which embraces the plate  8  and the edge of which is at a small distance from the wall of housing  1  in the mounted condition. To minimize the pressure fluid volume uptake of the second chamber  4 , a fill member  31  is arranged at the bottom of housing  1 .  
         [0020]    As can be taken from FIG. 2 in particular, the hydraulic port  5  that includes a fill or discharge opening  15  has a bore  10  designed as a stepped bore and comprising four portions. While two portions  11 ,  12  of equal diameter are used to guide the closure member  7 , a larger-diameter third portion  13  is provided between them, bounding an annular chamber  16  along with the closure member  7 . A fourth portion  14  designed at the bottom end of port  5  accommodates a circular clip  17  arranged at closure member  7  and used to limit the movement of the closure member  7  in the opening direction of the bottom valve  6 . The transition area between the portions  12 ,  13  is preferably a conical annular surface  18 . The above-mentioned annular chamber  16  is in connection with the second chamber  4  by means of radial passages  19 , while closure member  7  includes several radial flow ducts  20  being connected to the fill or discharge opening  15  of the hydraulic port  5 . The last mentioned connection is established through a cylindrical recess  21  designed in the closure member  7  and accommodating a valve spring  24  that preloads the closure member  7  in the opening direction of the bottom valve  6 . Two sealing elements  22 ,  23  arranged one behind the other at closure member  7  and being preferably configured as sealing cups that provide a sealing against the wall of portion  12  in the closing operation of the bottom valve  6 .  
         [0021]    A second cylindrical recess  25  that is provided at the end of the closure member  7  remote from the fill and discharge opening accommodates a spring, preferably a compression spring  26 , whose spring rate is considerably higher than the spring rate of the above-mentioned valve spring  24 . The compression spring  26  which is supported on the bottom of the cylindrical recess  25 , on the one hand, bears at its other end against a force-transmitting member  27 , which is slidably guided in the closure member  7  and cooperates with the plate  8  that closes the pleated bellows  2  in the closing operation.  
         [0022]    Closing of the bottom valve  6  takes place in two phases. Shortly before the evacuation of the chamber  4 , the plate  8  that closes the pleated bellows  2  starts touching the force-transmitting member  27 . Because the strength of the compression spring  26 , as mentioned above, exceeds the strength of the valve spring  24 , the closure member  7  upon further discharge of pressure fluid is displaced in opposition to the force generated by the valve spring  24  or urged downwards in the drawing until the outside sealing lip of the first sealing cup  22  moves into contact with the wall of the stepped bore portion  12  and, thus, prevents fluid circulation around the closure member  7 . The closure member  7  starts in this moment to fulfill the function of a hydraulic piston and is displaced further downwards by the residual pressure that prevails in the chamber  4 . This causes also displacement of the second sealing cup  23  into portion  12  sealing towards its wall.  
         [0023]    The bottom valve  6  is opened because liquid pressure fluid is pumped from the outside into the pressure fluid accumulator  1  according to the invention. When the charging pressure exceeds the residual pressure or internal pressure that prevails in the chamber  4  (ignoring the opening force of the compression spring  24  and closing force of the sealing cup friction), the closure member  7  is moved in the opening direction, discharging already its own displacement volume into the second chamber  4 . When the force-transmitting member  27  comes into abutment on the plate  8  of the media-separating element before the sealing cups  22  and  23  open the entry to chamber  4 , the dynamic pressure on the outside will rise because now the sealing cup  22  or the sealing cups  22  and  23  together must be overflown. By way of the effective surface of the closure member  7 , this dynamic pressure increase causes a force that is supported on the plate  8  of the media-separating element. When this flow force, caused by the fluid penetration through the narrow slot, becomes greater than the preloading force produced by spring  26 , the force applied to the plate  8  will be limited by this part because the force-transmitting member  27  is urged into the hydraulic port  5 . The result is that the sealing cups  22 ,  23  or their external lips will lift from the wall of the bore portion  12  and open the passage for the inflowing pressure fluid. Like in the closing operation, the contour of the annular chamber accommodating the sealing cup  22  will change only if the pressure difference applied to the sealing cup is insignificant. The closure member  7  is pressed further in an upward direction by the compression spring  14  until the force-transmitting member  27  again bears against the plate  8  closing the pleated bellows  2 . Upon further filling of the chamber  4 , the plate  8  will retreat, and the travel of the closure member  7  is limited by stop  17 .  
         [0024]    In the second embodiment of the bottom valve  6  illustrated in FIG. 3, like parts have been assigned like reference numerals. However, different from the embodiment shown in FIG. 2, the valve member  7  includes a bore  28  at its end close to plate  8 , said bore being used to guide a preferably tappet-shaped force-transmitting member  27   a  extending through the bore. At the end of the force-transmitting member  27   a  close to the fill and discharge opening  15 , the valve spring  24  is supported and thus performs both the function of the valve-opening spring and the function of the above-mentioned compression spring for reducing the force that acts on the closure member  7 . An auxiliary spring  29  interposed between the closure member  7  and the force-transmitting member  27   a  takes care of overcoming the friction of the force-transmitting member  27   a  in bore  28  so that no relative movement of the force-transmitting member  27   a  to the closure member  7  takes place in the closing operation. The sealing elements  22   a ,  23   a  arranged at the closure member  7  are configured as simple, robust O-rings in the embodiment shown. Another O-ring  30 , which is secured in the closure member  7  by means of a press-fitted steel ring  31 , is used to seal the force-transmitting member  27   a  in the closure member  7 . Another steel ring  32  press-fitted into closure member  7  is used as a stop for the stroke limitation of the opening movement of closure member  7 .  
         [0025]    In the third embodiment of the bottom valve  6  illustrated in FIGS. 4 a,b , the above-mentioned compression spring  26  is arranged outside the hydraulic port  5  coaxially relative to the closure member  7 . The open position of the bottom valve  6  is illustrated in FIG. 4 a , while FIG. 4 b  shows the closed position. The force-transmitting member  27   b  cooperates with a bead  33  designed at closure member  7  and includes a radial collar  34  on which the compression spring  26  is supported. The other end of the compression spring  26  is supported on a spring plate  35  secured to the closure member  7 . An O-ring  36  arranged at the closure member  7  and a plate-type seal  37  arranged below the spring plate  35  are used to seal the closure member  7  in relation to the hydraulic port  5 , said seal  37  being moved to abut on an annular surface  38  designed in the top area of the hydraulic port  5  in the closed condition of the bottom valve  6 . The hydraulic connection between the fill or discharge opening  15  and the second chamber  4  (not shown) (see FIG. 1) is established in the embodiment shown by means of longitudinal grooves  39  designed in closure member  7 . Another radial bead  40  designed in its bottom portion and additionally serving as a support of the valve spring  24  is used as a stop for the stroke limitation of the opening movement of the closure member  7 .  
         [0026]    The design of the fourth embodiment of the bottom valve  6  as shown in FIGS. 5 a,b  corresponds largely to the design according to FIG. 4. The closure member  7  is sealed in relation to the hydraulic port  5  by means of an O-ring  41  arranged in an annular groove of the hydraulic port  5  and cooperating with a large-diameter portion  42  of the closure member  7  as well as the plate-type seal mentioned with respect to FIG. 4 that is designated by reference numeral  43  in FIG. 5. The hydraulic connection between the fill or discharge opening  15  and the second chamber  4  (not shown) (see FIG. 1) is established in the embodiment shown by means of a bore portion  44  of large diameter that is designed in the area of the O-ring  41 .  
         [0027]    In the fifth variant of the bottom valve  6  of the invention as illustrated in FIGS. 6 a,b , the valve spring  24  and the above-mentioned compression spring  26  are arranged coaxially relative to each other in the area of the hydraulic port  5  that extends into the second chamber  4  (FIG. 1). The valve spring  24  preloading the closure member  7  in the opening direction has a larger diameter and is compressed between the hydraulic port  5  and a bowl-shaped force-transmitting member designated by reference numeral  45 . The compression spring  26  that preloads the force-transmitting member  45  in relation to the closure member  7  has a small diameter and, like in the third or fourth embodiment, is compressed between the force-transmitting member  5  and the spring plate  35  mentioned with respect to FIG. 4. The hydraulic connection between the fill or discharge opening  15  and the second chamber  4  (not shown) (see FIG. 1) is established in the embodiment shown by means of flow ducts provided in the hydraulic port  5  and limited by guiding ribs  46  designed on the closure member  7 . The mentioned connection is closed by means of a redundant sealing assembly secured at the closure member  7  and being formed of an O-ring  47  that seals in relation to the wall of bore  10  guiding the closure member  7 , and of a plate-type seal  48 . The plate-type seal  48  seals in relation to the hydraulic port  5 . Guiding ribs  53  designed at the closure member  7  are additionally used as stop elements for the limitation of the stroke of closure member  7  in the opening direction of the bottom valve.  
         [0028]    The design of the sixth embodiment of the bottom valve  6  as illustrated in FIGS. 7 a, b  corresponds largely to the embodiment according to FIG. 5, and the arrangement of the valve spring  24  and the compression spring  26  corresponds to the embodiment according to FIG. 6. However, only one O-ring  49  arranged in an annular groove of the hydraulic port  5  and cooperating with a large-diameter portion  50  of closure member  7  is used to seal the closure member  7  with respect to the hydraulic port  5 . The hydraulic connection between the fill or discharge opening  15  and the second chamber  4  (not shown) (see FIG. 1) is established in the embodiment shown by means of a large-diameter bore portion  51  designed in the area of the O-ring  49 . Guide ribs  52  designed on the closure member  7  are additionally used as stop elements for the limitation of the stroke of closure member  7  both in the opening and closing direction of the bottom valve  6 , and the ‘bottom’ stop is provided by a circular clip  60  inserted in port  5 . The stop may of course be also configured as e.g. a threaded sleeve screwed into port  5 .  
         [0029]    The seventh embodiment of the bottom valve  6  illustrated in FIGS. 8 a, b  corresponds largely to the embodiment according to FIG. 7. The only difference involves the type of sealing of the closure member  7  in relation to the hydraulic port  5  which is redundant in the embodiment shown and provided by two O-rings  54 ,  55  arranged one behind the other in annular grooves of the hydraulic port  5 , said O-rings cooperating with correspondingly configured large-diameter portions of closure member  7 .  
         [0030]    Of course, other sealing assemblies of the bottom valve  6  are also feasible within the limits of the invention, which consist of combinations of sealing elements arranged on the closure member  7  and in the hydraulic port  5 . Apart from the mentioned O-rings, multi-part seals such as metal rings with vulcanized rubber layers may also be used as sealing elements.  
         [0031]    The eighth embodiment of the bottom valve  6  illustrated in FIGS. 9 a  to  d  corresponds largely to the embodiment according to FIG. 8. A means is provided in this embodiment, however, protecting the redundantly configured sealing assembly  56 ,  57  of the closure member  7  against being damaged by a high fill pressure in critical phases of operation of the bottom valve  6 . For this purpose, an annular part  58  made of plastics, e.g. Teflon, or metal, is arranged in the hydraulic port  5  and limits an annular slot or a defined flow cross-section along with a portion  71  of the closure member  7 . When the closure member  7  is moved during the filling operation from the closed valve piston (FIG. 9 a ) into the opening direction, a defined pressure fluid volume will flow through the above-mentioned annular slot so that the pressure acting on the sealing elements  56 ,  57  is reduced.  
         [0032]    In the ‘critical’ actuating position depicted in FIG. 9 b , the sealing elements  56 ,  57  move in the direct vicinity of edges  66 ,  67  designed in the hydraulic port  5 , leaving the areas of the edges as the opening movement (FIG. 9 c ) continues. The slots produced at the edges  66 ,  67  are considered critical herein, through which slots the sealing elements  56 ,  57  would be slid under the effect of the otherwise high fill pressure and damaged or destroyed thereby. Only when the sealing elements  56 , 57  are disposed outside the ‘critical’ area will the annular part  58  release the full volume flow through the sealing elements  56 ,  57  (FIG. 9 d ).  
         [0033]    The representation of the individual phases of operation of the ninth embodiment of bottom valve  6  as shown in FIGS. 10 a  to  d  corresponds to the representation of the above-described embodiment according to FIG. 9. The means explained with respect to the embodiment according to FIG. 9, however, herein comprises a valve assembly  59 , which is actuated by the opening movement of the closure member  7  of bottom valve  6 . The valve assembly  59  in the embodiment shown is configured as a seat valve whose seat is designed in the closure member  7 . Because the function of the valve assembly  59  corresponds to the mode of operation of the above-mentioned means and can undoubtedly be taken from the representation according to FIGS. 10 a - d , it need not be explained in detail.  
         [0034]    The illustration of the tenth embodiment of the bottom valve  6  as shown in FIGS. 11 a, b  corresponds to the representation of the above-described embodiments according to FIGS.  4  to  8 , FIG. 11 a  showing the closed position of the bottom valve  6  and FIG. 11 b  showing the open position. The design of the embodiment shown basically corresponds to that of the ninth embodiment according to FIG. 10. The basic differences include above all the design of the closure member  7  and the function of the above-mentioned valve assembly  59 . The closure member  7  is configured as a stepped piston and includes a first step  72  of small diameter and a second step  73  of larger diameter. The first step  73  carries the first sealing element  74  that is designed as a sealing sleeve with an L-shaped cross-section. An annular chamber  75  confined by the first step  72  in the hydraulic port  5  is connected by way of a transverse bore  76  to a flow duct  77  that axially extends in closure member  7  and whose end forms the seat of the valve assembly  59  designed as seat valve. In contrast thereto, the second step  73  confines in the bore of the hydraulic port  5  a second annular chamber  78  that is in connection with the flow duct  76  by means of a second transverse bore  79 . The second sealing element  80  arranged on the second step  73  represents a combination formed of an O-ring and a back ring.  
         [0035]    It can be taken from the illustration that the second step  73  produces an increase of the hydraulic pressure in the annular chamber  75  during the filling operation, whose value roughly corresponds to the value of the pressure that prevails in the pressure fluid accumulator. It is achieved thereby that the first sealing element  74  is pressure-balanced and there is no risk of damage by an excessive pressure. When the hydraulic pressure in the annular chamber  75  reaches a predeterminable value, the valve assembly  59 , which additionally performs the function of a pressure relief valve, is briefly opened so that the pressure in the annular chamber  75  is reduced to an allowable value.  
         [0036]    In the eleventh embodiment of the bottom valve  6  of the invention as illustrated in FIGS. 12 a,b , the initially defined object of the invention is achieved by hydraulic means representing a series arrangement of two valve assemblies  81 ,  82  in the example shown. The first valve assembly  81  is formed of passages  83  designed in closure member  7  and a sealing element  84  that is immovably arranged in the hydraulic port  5 , while the second valve assembly  82  is designed as a central valve arranged in closure member  7 . The valve spring  86  of this central valve is preferably designed so that only a low differential pressure is necessary to open the central valve. The sealing element  85  arranged on the closure member  7  is designed as a sealing cup. The passages  83  are in connection to the fill and discharge opening  15  so that when they override the sealing element  84  during the opening movement of the closure member  7 , the pressure fluid flows into an annular chamber  87  limited by the closure member  7  in the hydraulic port  5  and the filling pressure is applied to the central valve  82 . Due to the effect of the pressure difference between the pressure in the annular chamber  87  and the pressure prevailing within the pressure fluid accumulator, the central valve  82  is opened and the filling pressure acting on the closure member  7  reduced.