Abstract:
A hydraulic accumulator includes: a pressure vessel; a hose which is situated within the pressure vessel, for receiving a first medium; a gap, which is formed between the pressure vessel and the hose, for receiving a second medium; and at least one connection for supplying and discharging the first or the second medium under pressure into or out of the hose or the gap, the supply of the first medium resulting in the compression of the second medium.

Description:
BACKGROUND INFORMATION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a hydraulic accumulator as well as a method for ascertaining a state of charge of a hydraulic accumulator. 
         [0003]    2. Description of the Related Art 
         [0004]    Hydraulic accumulators are typically used to store large amounts of energy. In hydraulic hybrid vehicles, hydraulic accumulators are, for example, used to store the energy which is, for example, generated when the wheels are braked and to release the energy which is, for example, needed when the vehicle is accelerated. A hydraulic accumulator of this type is described in published German patent application document DE 10 2006 060 078 A1, for example. 
         [0005]    Hydraulic accumulators which have an accumulator bladder are known, in particular, from the related art. The bladder is usually made of rubber and provides for a separation between a gas and a hydraulic fluid in the hydraulic accumulator. Hydraulic accumulators of this type are usually situated perpendicularly, i.e., the pressure vessel receiving the hydraulic fluid, the gas, and the accumulator bladder extends essentially perpendicularly to the ground. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The hydraulic accumulator of the present invention offers the advantage over the conventional approaches that a hose is easily manufacturable. Furthermore, a hydraulic accumulator of this type is scalable using only little effort, since the length of the hose is easily adjustable. Furthermore, hoses may generally be folded in a predictable manner if they are held horizontally, i.e., the hose extends essentially in parallel to the ground. It is true that in the long-term folding bears the risk of damaging the hose. Since, however, the folding is predictable, the hose may be laid out accordingly to avoid such damage. The hydraulic accumulator according to the present invention and its hose may thus also be operated horizontally. 
         [0007]    The method of the present invention has the advantage over the conventional approaches that the state of charge of a hydraulic accumulator may be ascertained in a simple manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Exemplary embodiments of the present invention are illustrated in the drawing and explained in greater detail in the description that follows. 
           [0009]      FIG. 1  shows a hydraulic accumulator according to one exemplary embodiment of the present invention in a longitudinal sectional view. 
           [0010]      FIG. 2  shows a section A-A from  FIG. 1 . 
           [0011]      FIG. 3  shows a variation of  FIG. 2 . 
           [0012]      FIG. 4  shows a variation of  FIG. 3 . 
           [0013]      FIG. 5  shows a diagram which illustrates a charge characteristic of the hydraulic accumulator according to  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    In the figures, identical reference numerals identify identical components or components having an identical function, unless otherwise indicated. 
         [0015]      FIG. 1  shows a hydraulic accumulator  1  according to one exemplary embodiment of the present invention in a longitudinal sectional view.  FIG. 2  shows a section A-A from  FIG. 1 . 
         [0016]    The hydraulic accumulator has a pressure vessel  2 . The latter is dimensionally stable and for this purpose is made of steel, for example. The pressure vessel has a base body  4  which extends along a longitudinal axis  3  and has an essentially annular cross section (see  FIG. 2 ). Base body  4  has a neck  5  at its one end. Base body  4  is closed by a base plate  6  at its opposite end. Another base plate could also be provided instead of neck  5 . 
         [0017]    A hose  7  is situated within pressure vessel  2 . Hose  7  is made of a flexible and elastic material such as rubber. The elasticity of hose  7  may be advantageously used to influence the charge characteristic of hydraulic accumulator  1 , as will be described later. 
         [0018]    Preferably, hose  7  is produced with the aid of extrusion. In this way, hose  7  may be easily manufactured in any desirable length so that longer or shorter hydraulic accumulators  1  may be built without any problems. 
         [0019]    Hose  7  has in its filled state  7 ′, shown as a solid line in  FIG. 1 , a fundamentally annular cross section  11 , as illustrated in  FIG. 2 . According to the present exemplary embodiment, cross section  11  is, however, thicker at diametrically opposed points  12  and thinner at diametrically opposed points  13  in deviation from the annular shape. 
         [0020]    One end  14  of hose  7  extends through an opening  15  formed by neck  5  of pressure vessel  2 . A plug element  16  is pressed into end  14  of hose  7  so that plug element  16  seals end  14  of hose  7  internally and also seals end  14  of hose  7  externally against opening  15  in neck  5  of pressure vessel  2 . Plug element  16  has a connection  17  with the aid of which a first medium  18 , e.g., a hydraulic fluid, may be supplied to interior  21  of hose  7 . Furthermore, hydraulic fluid  18  may be discharged again from interior  21  with the aid of connection  17 . 
         [0021]    End  22  of hose  7  which is opposite to end  14  extends through an opening  23  in base plate  6  of pressure vessel  2 . Another plug element  24  is pressed into end  22  of hose  7  so that this plug element seals end  22  of hose  7  internally and also seals end  22  externally against opening  23 . 
         [0022]    Plug elements  16  and  24  do not have to be pressed into ends  14  and  22  of hose  7 , respectively. Alternatively, end  14  may be sealingly glued or otherwise connected to plug element  16  and opening  15 , and likewise end  22  to plug element  24  and opening  23 . 
         [0023]    Preferably, plug elements  16  and  24  each have a rounding  25  and  26 , respectively, which bulges into interior  21  of hose  7 . Roundings  25  and  26  are supposed to prevent damage to hose  7  or abrasion thereof in its empty state labeled with reference numeral  7 ″ in  FIG. 1 . Roundings  25  and  26  preferably each have an approximately parabolic shape. Plugs  16 ,  24  are additionally fixed in the axial direction (not shown); the fixing may be necessary due to the high internal pressure. 
         [0024]    Empty state  7 ″ of hose  7  is also illustrated in  FIG. 2 , hose  7  having an essentially oval shape of cross section  27 . To reliably achieve this type of folding of hose  7  to obtain the illustrated oval shape of cross section  27  in its empty state  7 ″, hose  7  is designed to have the previously described thicker and thinner points  12  and  13 , respectively. 
         [0025]    Base plate  6  of pressure vessel  2  has a connection  31 . Connection  31  allows a second medium  30 , for example a gas, to be supplied to and discharged from a gap  32  formed between pressure vessel  2  and hose  7 . In the present case, gap  32  is designed as an annular space and extends along longitudinal axis  3 . 
         [0026]    To obtain a desired charge characteristic, an additional pressure vessel for gas (not illustrated) may be connected to connection  31  of pressure vessel  2 . 
         [0027]    Hydraulic accumulator  1  according to  FIG. 3  differentiates itself from that according to  FIGS. 1 and 2  solely in that hose  7  is designed to have external longitudinal grooves  28 .  FIG. 3  shows here an elastically stretched state  7 ″′ of hose  7 , which is also shown in  FIG. 1 . Longitudinal grooves  28  and hose  7  are illustrated exaggeratedly large and thick for the sake of better understanding. 
         [0028]    Hydraulic accumulator  1  according to  FIG. 4  differentiates itself from that according to  FIGS. 1 and 2  solely in that hose  7  is designed to have internal longitudinal grooves  29 .  FIG. 4  shows here empty state  7 ″ of hose  7 , which is also shown in  FIG. 1 . Longitudinal grooves  29  and hose  7  are illustrated exaggeratedly large and thick for the sake of better understanding. 
         [0029]    Following the previous, essentially constructive description of hydraulic accumulator  1 , its mode of operation will now be described. 
         [0030]    The energy generated when the motor vehicle is braked may, for example, be used to pump hydraulic fluid  18  under pressure through connection  17  of hydraulic accumulator  1  into interior  21  of hose  7 . During this process, hose  7  expands from its empty state  7 ″ to its filled state  7 ′ (see  FIG. 1 ). 
         [0031]    Internal longitudinal grooves  29  in hose  7  are used here to prevent opposite hose walls  33  and  34  from sticking together and to thus ensure a reliable filling of hose  7 . 
         [0032]    While hose  7  expands, gas  30  located in gap  32  is compressed. 
         [0033]    In a diagram,  FIG. 5  shows a charge characteristic of hydraulic accumulator  1 . “Charge characteristic” is understood in the present case as the characteristic of the pressure in hydraulic fluid  18  or in gas  30  as a function of the state of charge, i.e., as a function of the degree of filling of hose  7 . As is apparent from  FIG. 5 , an increasing pressure in hydraulic fluid  18  is necessary to further compress the gas in gap  32 . The pressure characteristic between empty state  7 ″ and filled state  7 ′ is labeled with reference symbol A in  FIG. 5 . If the supply of hydraulic fluid is continued; hose  7  must stretch elastically in order to deform from its filled state  7 ′ to its elastically stretched state  7 ″′. The pressure characteristic as a function of the state of charge between filled state  7 ′ of hose  7  and elastically stretched state  7 ″′ is labeled with reference symbol B in  FIG. 5 . This pressure characteristic B may be influenced by appropriately selecting the elasticity of hose  7 , for example, by designing the hose from a different material and/or to have a thicker or thinner wall. 
         [0034]    The pressure change in a transition area “C” (and/or its first mathematical derivative) between lines A and B may be detected in order to determine that a state of charge X has been reached. State of charge X corresponds to filled state  7 ′ of hose  7 . The pressure change is advantageously measured with increasing charge, i.e., filling, or discharge, i.e., emptying, of hydraulic accumulator  1  and compared to a predetermined pressure change which is provided for state of charge X. 
         [0035]    If hose  7  is completely filled in its elastically stretched state  7 ′″ the hose is in contact with the interior walls of pressure vessel  2 , as illustrated in  FIG. 3 . Now, in order to prevent gas blankets from forming between hose  7  and pressure vessel  2 , the hose has longitudinal grooves  28  so that gas  30  may be distributed evenly along longitudinal axis  3  of hose  7 . Of course, it is also conceivable to additionally provide transversal grooves. 
         [0036]    Although the present invention was described here concretely with reference to exemplary embodiments, it is not limited thereto, but may be modified in various ways. 
         [0037]    In particular, hydraulic fluid  18  may also be provided in gap  32 , and gas  30  in interior  21 . In this case, hydraulic fluid  18  would be supplied and discharged via connection  31 , for example. The other pressure vessel (not illustrated) for gas (also referred to as secondary gas volume) could then be connected to connection  17 . 
         [0038]    Furthermore, plug element  16  and pressure vessel  2  could be made as one piece and/or base plate  6  and plug  24  could be made as one piece.