Patent Abstract:
A volume accumulator ( 15 ), including a guide housing ( 33 ) and a separating element ( 34 ), wherein the separating element ( 34 ) is slidably mounted on an inner lateral face of the guide housing ( 33 ). At least one indentation ( 41 ) is located on the guide housing ( 33 ), with the indentation protruding into the guide housing ( 33 ), wherein in the direction of the separating element ( 34 ) the indentation ( 41 ) has an open end that serves as a stop for the separating element ( 34 ).

Full Description:
FIELD OF THE INVENTION 
     The invention relates to a volume accumulator having a guide housing and a dividing element, wherein the dividing element is mounted in a displaceable manner on an inner lateral surface of the guide housing. 
     BACKGROUND 
     Volume accumulators are used for example in internal combustion engines in order to assist in the supply of pressurized medium to a hydraulic consumer, for example to a camshaft adjuster or an electrohydraulic valve actuating device. Camshaft adjusters are known for example from DE 195 29 277 A1 or from EP 0 806 550 A1. 
     A volume accumulator is disclosed for example in DE 10 2007 041 552 A1. The volume accumulator has a hollow cylindrical guide housing and has a dividing element, in the illustrated embodiment a pot-shaped piston, which is held in an axially displaceable manner in the guide housing and which divides the interior of the guide housing into a storage space and a complementary space. When the piston is acted on with pressurized medium, it is displaced counter to the force of a spring element in the direction of a stop, as a result of which the volume of the storage space increases at the expense of the volume of the complementary space. Here, the displacement travel of the piston is limited in that an open end of a casing portion of the pot-shaped piston comes to bear against an annular stop which is formed separately from the guide housing. The annular stop bears against a radially running wall on an axial end, on which the spring element is simultaneously supported, of the guide housing. 
     SUMMARY 
     It is an objective of the invention to provide a volume accumulator, the manufacturing expenditure for which should be reduced. 
     The object is achieved according to the invention in that at least one indentation is formed on the guide housing, which indentation projects into the guide housing, wherein the indentation has, in the direction of the dividing element, an open end which serves as a stop for the dividing element. 
     The volume accumulator has a dividing element, for example a piston, which is mounted in a displaceable manner within a guide housing and which divides a storage space from a complementary space. When said dividing element is acted on by pressurized medium, it is displaced within the guide housing in the direction of a stop which limits the displacement travel of the dividing element in that the latter comes to bear against the stop. The stop secures the dividing element so as to prevent it from inadvertently emerging from the guide housing during the operation thereof. Furthermore, through suitable positioning of the stop between the ends of the guide housing, it is possible to utilize suitable spring strengths and spring lengths and thereby suitably configure the volume accumulator characteristics. 
     It is provided here that the stop is formed from the material of the guide housing. For this purpose, in the guide housing, which is for example of hollow cylindrical design, a slot is provided which runs along a discontinuous line. Here, the slot runs, at least in regions, in a plane perpendicular to the displacement direction of the piston. The slot may be formed into the guide housing by punching or fine blanking, for example. Provided on the guide housing in the region of the slot is an indentation which projects into the interior of the guide housing. Here, an open end, generated by the slot, of the indentation faces the piston and serves as a stop for the latter. The open end means the region which was connected to the guide housing before the formation of the slot into said guide housing. 
     In this embodiment, the stop is firstly formed in one piece with the guide housing, such that there is no requirement for additional components. Secondly, there is no material connection between the stop surface and that region of the guide housing which lies in the direction of the piston, such that said transition region is designed to be rectangular, without a radius or phase. It is thus ensured that the dividing element does not become jammed against the stop. Furthermore, the abutment of two surfaces arranged perpendicular to the displacement direction prevents the piston from passing under the indentation and becoming jammed, or the indentation from being pressed outward. 
     The indentation may take on a multiplicity of forms. Embodiments are for example conceivable in which a slot is formed into the guide housing, which slot is arranged entirely in a plane perpendicular to the displacement direction of the piston. The indentation is subsequently formed into the guide housing in the region of the slot. 
     Likewise conceivable are embodiments in which the indentation is formed as a lug. Here, a slot which deviates from a straight line is formed into the guide housing, which slot forms a lug which is connected to the guide housing. This lug may for example be triangular or tetragonal and may if appropriate be bulged corresponding to the shape of the guide housing, and projects into the guide housing. 
     In one physical embodiment of the invention, it is provided that a spring element is arranged in the guide housing, which spring element extends through the region of the indentation, wherein the indentation has a guide portion for the spring element, the length of which guide portion in the direction of force of the spring element is greater than the spacing between two windings of the spring element. The guide portion provides a guide surface for the spring element which exerts a force on the piston counter to the force of the pressurized medium. The spring element may be designed for example as a helical or spiral compression spring. Here, through suitable selection of the length of the guide portion, it is ensured that there is always one winding of the spring element arranged in said region, and therefore the spring element is provided with adequate guidance such that the spring windings do not become jammed against the stop of the lug. 
     The dividing element may for example be designed as a pot-shaped piston with a base and an adjoining casing portion. The guide housing and the piston are advantageously produced by non-cutting processes from in each case one sheet-metal blank, for example by means of a deep-drawing process. Here, the casing portion of the piston and the inner lateral surface of the guide housing may be designed to be cylindrical or polygonal in cross section, for example. The base of the piston serves as a pressure surface, which is acted on with a force by the pressurized medium flowing in, as a result of which the piston is displaced. The lateral surface serves for mounting the piston in the guide housing, wherein the open end of the casing portion comes to bear against the stop when the volume accumulator is completely full. Furthermore, the sealing of the storage space with respect to the complementary space is realized by means of close-tolerance play between the casing portion and the inner lateral surface of the guide housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the invention will emerge from the following description and from the drawings, in which exemplary embodiments of the invention are illustrated in simplified form. In the drawings: 
         FIG. 1  shows an internal combustion engine merely in highly schematic form, 
         FIG. 2  shows a longitudinal section through a camshaft adjuster which is fastened to a camshaft in which a first embodiment of a volume accumulator is arranged, 
         FIG. 3  shows a cross section through the camshaft adjuster from  FIG. 2  along the line III-III, wherein the central screw is not illustrated, 
         FIG. 4  shows the detail X from  FIG. 2  without a camshaft, 
         FIG. 5  shows a cross section through the volume accumulator along the line V-V in  FIG. 4 , 
         FIG. 6  shows a perspective view of the first embodiment of a volume accumulator, 
         FIG. 7  shows a perspective view of a second embodiment of a volume accumulator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts an internal combustion engine  1 , wherein a piston  3  is shown which is seated on a crankshaft  2  and which is arranged in a cylinder  4 . In the embodiment illustrated, the crankshaft  2  is connected via in each case one traction mechanism drive  5  to an intake camshaft  6  and an exhaust camshaft  7 , wherein a first and a second camshaft adjuster  11  can effect a relative rotation between the crankshaft  2  and the camshafts  6 ,  7 . Cams  8  of the camshafts  6 ,  7  actuate one or more intake gas exchange valves  9  or one or more exhaust gas exchange valves  10 . Provision may also be made for only one of the camshafts  6 ,  7  to be equipped with a camshaft adjuster  11 , or for only one camshaft  6 ,  7  to be provided, which is provided with a camshaft adjuster  11 . 
       FIGS. 2 and 3  show a camshaft adjuster  11  in longitudinal section and cross section. Furthermore,  FIG. 2  shows a volume accumulator  15  which is arranged in a camshaft  6 ,  7  which is connected in a rotationally conjoint manner to the camshaft adjuster  11 . 
     The camshaft adjuster  11  comprises a drive element  14 , a driven element  16  and two side covers  17 ,  18  which are arranged on the axial side surfaces of the drive input element  14 . The driven element  16  is designed in the form of a vane wheel and has a hub element  19  which is of substantially cylindrical design and from the external cylindrical lateral surface of which, in the embodiment illustrated, five vanes  20  extend outward in the radial direction. 
     Five pressure spaces  22  are provided within the camshaft adjuster  11 , wherein a vane  20  projects into each pressure space  22 . Here, the vanes  20  are designed so as to bear both against the side covers  17 ,  18  and also against the circumferential wall  21 . Each vane  20  thereby divides the respective pressure space  22  into two oppositely-acting pressure chambers  23 ,  24 . 
     Formed on an external lateral surface of the drive element  14  is a sprocket  12  via which torque can be transmitted from the crankshaft  2  to the drive element  14  by means of a chain drive (not illustrated). The driven element  16  is connected in a rotationally conjoint manner to the camshaft  6 ,  7  by a central screw  13 . 
     The driven element  16  is arranged so as to be rotatable relative to the drive element  14  over a defined angle range. By supplying pressurized medium to one group of pressure chambers  23 ,  24  and discharging pressurized medium from the other group, the phase position of the drive element  14  with respect to the driven element  16  (and therefore the phase position of the camshafts  6 ,  7  with respect to the crankshaft  2 ) can be varied. By supplying pressurized medium to both groups of pressure chambers  23 ,  24 , the phase position can be held constant. 
     The camshaft  6 ,  7  has, in the region of a camshaft bearing  32 , a plurality of openings  28  via which pressurized medium delivered by a pressurized medium pump  37  passes into the interior of said camshaft. Formed within the camshaft  6 ,  7  is a pressurized medium path  29  which communicates at one side with the openings  28  and at the other side with a control valve  27  which serves for the supply of pressurized medium to the camshaft adjuster  11 . The control valve  27  is arranged in the interior of the central screw  13 . Through use of the control valve  27 , pressurized medium can be selectively conducted to the first or second pressure chambers  23 ,  24  and discharged from the other pressure chambers  23 ,  24  in each case. 
     Provided in the interior of the central screw  13  is a pressurized medium duct  30  which communicates at one side with the pressurized medium path  29  and at the other side with a cavity  31  of the hollow camshaft  6 ,  7 . The pressurized medium duct  30  is formed as an axial bore which extends through the threaded portion of the central screw  13 . 
     The volume accumulator  15  is arranged in the cavity  31 . The volume accumulator  15  comprises a guide housing  33 , a dividing element  34  and a force accumulator which, in the embodiment illustrated, is designed as a spring element  35  in the form of a helical compression spring. The guide housing  33  is connected in a non-positively locking manner to a wall  36  of the cavity  31 . Embodiments are also conceivable in which the guide housing  33  is connected in a cohesive or positively locking manner to the wall  36 . 
     The dividing element  34  is arranged in an axially displaceable manner in the interior of the guide housing  33 , wherein, in the embodiment illustrated, said dividing element is formed as a pot-shaped piston with a base  25  and a casing portion  26 . The dividing element  34  is mounted by the casing portion  26  in an axially displaceable manner in the guide housing  33 . The outer lateral surface of the dividing element  34  is matched to the inner lateral surface of the guide housing  33  in such a way that the guide housing  33  is separated in a pressure-medium-tight manner into a storage space  45  axially in front of and a complementary space  46  behind the base  25  of the dividing element  34 . 
     The spring element  35  is supported at one side on a spring support  39  ( FIG. 4 ), which is formed on that end of the guide housing  33  which faces away from the camshaft adjuster  11 , and at the other side on the base  25  of the dividing element  34 . The spring element  35  therefore loads the dividing element  34  with a force in the direction of the pressurized medium duct  30 . The spring support  39  is formed as a radial indentation  47  of the guide housing  33 . For this purpose, the cylindrical guide housing  33  has formed into it a first slot  40  which runs in the circumferential direction of the guide housing  33 . The guide housing  33  is subsequently deformed radially inward in the region between the first slot  40  and the end facing away from the camshaft. The depth of the indentation  47  thereby produced is selected such that the spring element  35  bears, even at maximum spring eccentricity, against the open end, which has been separated from the guide housing  33  by the first slot  40 , of the spring support  39 . 
     The displacement travel of the dividing element  34  is limited in the direction of the pressurized medium duct  30  by an annular, radially inwardly running portion of the guide housing  33 , which portion engages around a housing opening  38  through which pressurized medium can be supplied to the volume accumulator  15 . The displacement travel of the dividing element  34  is limited in the direction of the spring support  39  by a stop. The stop is designed, between the axial ends of the guide housing  33 , in the form of three indentations  41  which are formed in one piece with and project into the guide housing  33  ( FIGS. 4-6 ). Embodiments are likewise conceivable which have more or fewer indentations. Each indentation  41  has an open end on the side facing toward the dividing element  34 , wherein the open end has a surface perpendicular to the direction of movement of the dividing element  34 . The production of the indentations  41  takes place in two stages. Firstly, there is formed into the guide housing  33  a second slot  42  which runs in the circumferential direction of the guide housing  33 . Subsequently, the material of the guide housing  33  in the region of the second slot  42  is plastically deformed into the guide housing, thus forming the indentation  41 . 
     Each indentation  41  projects into the guide housing  33  such that the open end faces the open end of the casing portion  26  of the dividing element  34  in the displacement direction of the latter. These open ends of the indentations  41  therefore serve as a stop for the dividing element  34 . 
     Furthermore, each indentation  41  has a guide portion  43  which extends in the axial direction and runs parallel to the axis of the spring element  35 . Here, the diameter of the spring element  35  is selected such that said spring element bears against the guide portions  43  when it is in the compressed state. The spring element  35  is therefore mounted by means of the guide portions  43 , whereby the radial position of the spring element  35  is defined. The length L of the guide portion  43  is greater than the spacing between two spring windings in the relaxed state. It is thereby ensured that, on account of the mounting of the spring element  35  on the guide portions  43 , the spring element  35  does not become misaligned or jammed against the stop of the indentation  41 . 
     In the embodiment illustrated, the guide housing  33  and the dividing element  34  are formed as sheet-metal parts produced for example by means of a non-cutting production process, for example a deep-drawing process. Aside from low production costs, this has the advantage that, by means of said shaping process, the bearing surfaces of the casing portion  26  and of the guide housing  33  can be produced with such precision that they do not require any reworking. 
     In an alternative embodiment of a volume accumulator  15 , the second slot  42  describes a curved line with two ends, such that a lug  44  is formed which projects into the guide housing  33 . A volume accumulator  15  of said type is illustrated in  FIG. 7  in a perspective view. In this embodiment, a rectangular lug  44  which projects into the guide housing  33  is formed by means of a U-shaped second slot  42 . Here, one limb of the U-shaped slot  42  runs in a plane perpendicular to the movement direction of the dividing element  34 , such that the stop is formed. Aside from the embodiment illustrated in  FIG. 7 , in which the lug  44  is connected to the guide housing  33  in the circumferential direction, embodiments are also conceivable in which the lug  44  merges into the guide housing  33  in the axial direction. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Internal combustion engine 
           2  Crankshaft 
           3  Piston 
           4  Cylinder 
           5  Traction mechanism drive 
           6  Intake camshaft 
           7  Exhaust camshaft 
           8  Cam 
           9  Inlet gas exchange valve 
           10  Outlet gas exchange valve 
           11  Camshaft adjuster 
           12  Sprocket 
           13  Central screw 
           14  Drive element 
           15  Volume accumulator 
           16  Driven element 
           17  Side cover 
           18  Side cover 
           19  Hub element 
           20  Vane 
           21  Circumferential wall 
           22  Pressure space 
           23  First pressure chamber 
           24  Second pressure chamber 
           25  Base 
           26  Casing portion 
           27  Control valve 
           28  Openings 
           29  Pressurized medium path 
           30  Pressurized medium duct 
           31  Cavity 
           32  Camshaft bearing 
           33  Guide housing 
           34  Dividing element 
           35  Spring element 
           36  Wall 
           37  Pressurized medium pump 
           38  Housing opening 
           39  Spring support 
           40  First slot 
           41  Indentation 
           42  Second slot 
           43  Guide portion 
           44  Lug 
           45  Storage space 
           46  Complementary space 
           47  Indentation 
         L Length

Technology Classification (CPC): 5