Abstract:
A device ( 11 ) for the variable adjusting of the control timing of gas exchange valves ( 9, 10 ) of an internal combustion engine ( 1 ) with a drive element ( 13 ), an output element ( 14 ), at least one pressure chamber ( 23 ) and a volume accumulator ( 31 ), wherein the output element ( 14 ) is arranged in a rotatable manner to the drive element ( 13 ), and the pressure chamber ( 23 ) is bordered at least partially by these components ( 13, 14 ), wherein a phase position between the output element ( 14 ) and the drive element ( 13 ) can be variably adjusted by the pressure medium supply to or pressure medium removal from the pressure chamber ( 23 ). Pressure medium lines ( 25   a, b, p ) are provided by which the pressure medium can be supplied to the pressure chamber ( 23 ) or removed therefrom. The volume accumulator ( 31 ) has at least one housing ( 32 ) and a displaceable separating element ( 33 ) therein that separates a supply chamber ( 34 ), which connects to one of the pressure medium lines ( 25   a, b, p ), from a ventilated complementary space ( 35 ). The separating element ( 33 ) is displaced in the housing ( 32 ) by the admission of the pressure medium in the supply chamber ( 34 ) in such a way that the volume of the supply chamber ( 34 ) increases at the expense of the complementary space ( 35 ).

Description:
BACKGROUND 
     The invention relates to a device for the variable adjustment of control timing of gas exchange valves of an internal combustion engine with a drive element, an output element, at least one pressure chamber, and a volume accumulator, with the output element being arranged rotatably in reference to the drive element, and the pressure chamber being partially limited by said parts, with a phase position between the drive element and the output element being adjustable in a variable fashion by supplying and/or removing pressure medium from the pressure chamber, with pressure medium lines being provided via which pressure medium can be supplied to the pressure chamber or from which it can be removed, with the volume accumulator comprising at least one housing and a separating element that can be displaced therein, which separates a supply chamber communicating with the pressure medium lines from a ventilated complementary chamber, with by the impingement of pressure medium from the supply chamber, the separating element is displaced in the housing such that the volume of the supply chamber increases at the expense of the complementary chamber. 
     In modern internal combustion engines devices are used for variably adjusting the control timing of gas exchange valves, in order to allow variable designing of the phase position of a camshaft in reference to a crankshaft within a defined angular range between a maximum early and a maximum late position. For this purpose, the device is integrated in a drive train by which torque is transferred from the crankshaft to the camshaft. This drive train can be realized as a belt, chain, or gear drive, for example. 
     Such a device is known for example from DE 10 2007 041 552 A1. The device comprises a phase position device with a drive element which is in a drive connection with the crankshaft, and which is connected to an output element connected to the camshaft in a torque-proof fashion. Furthermore, the phase position device comprises several pressure chambers with each of the pressure chambers being divided by an impeller into two mutually influencing pressure chambers. By the supply of pressure medium to and/or draining of pressure medium from the pressure chambers, the blades inside the pressure chambers are displaced, leading to a change of the phase position between the output element and the drive element. 
     The supply of pressure medium to and/or the pressure medium drained from the pressure chambers is controlled via a hydraulic circuit comprising a pressure medium pump, a pressure medium reservoir, a control valve, and several pressure medium lines. The control valve comprises several pressure medium connectors, with one pressure medium line connecting the pressure medium pump to the control valve. One additional pressure medium line each connects one of the operating connections of the control valve to one group each of the oppositely operating pressure chambers. 
     During operation of the internal combustion engine alternating torques impinge the camshaft, each of which is caused by the cams rolling over gas exchange valves pre-stressed by a valve spring. These torques are transferred to the phase adjustment device and act by braking and/or accelerating the adjustment speed of the phase position. Here, when opening the gas exchange valve a phase adjustment occurs in the direction of a later control timing and when closing the gas exchange valve a phase adjustment is supported in the direction of an earlier control timing. During the phases in which the alternating torques support the phase adjustment the need for pressure medium of the phase adjustment device increases rapidly and can exceed the volume flow rate transported by the pressure medium pump. In this case, the phase adjustment speed is not determined by the supporting alternating torque but by the volume flow rate of the pressure medium pump. In this case, the supporting contribution of the alternating torques cannot be fully utilized. The smaller the dimensioning of the pressure medium pump the more distinct is this negative effect. 
     In each operating phase of the internal combustion engine the volume flow rate required by the phase adjustment device in order to ensure the function of the phase position adjustment the pressure medium pump must supply. For this purpose a volume accumulator is provided in DE 10 2007 041 552 A1, which communicates with the pressure medium line connecting the pressure medium pump with the control valve. In phases in which the pressure medium required by the phase adjustment device is lower than the volume of pressure medium transported by the pressure medium pump, the volume accumulator is filled. Here, a piston inside a housing is displaced against a force accumulator, in the exemplary embodiment shown a pressure spring. In these phases the force accumulator is stressed, i.e. the force accumulator accepts an amount of energy which can be resupplied to the hydraulic system. When the system pressure falls, the volume accumulator empties under the influence of the relaxing force accumulator into the hydraulic circuit and thus supports the phase adjustment of the camshaft in reference to the crankshaft. 
     In the exemplary embodiment shown it is disadvantageous that due to the stressed pressure spring, the emptying of the volume accumulator begins to occur already at a point of time at which the volume flow rate supplied by the pressure medium pump is sufficient to ensure the adjustment. The volume of pressure medium displaced in this phase from the volume accumulator is no longer available in the phases of insufficient supply of the phase adjustment device. 
     SUMMARY 
     The invention is based on the objective of providing a device for variably adjusting the control timing of gas exchange valves of an internal combustion engine with the braking effect acting upon the phase adjustment device, caused by insufficient supply of pressure medium, is minimized without requiring enlarging the size of the pressure medium pump of the internal combustion engine. 
     The objective is attained according to the invention such that the volume accumulator comprises a force accumulator which is stressed when the supply chamber is filled. 
     The phase adjustment device is embodied for example in the form of an adjustment impeller and comprises a drive element which for example is driven via a traction mechanism or gear drive by a crankshaft of the internal combustion engine. Furthermore, an output element is provided, which has a constant phase position in reference to the camshaft, for example via a friction, force, or material-fitting connection, or a screwed connection thereto in a torque-proof fashion. The output element is arranged rotational in reference to the drive element and at least partially accepted therein. Within the phase adjustment device at least one pressure chamber is provided. By supplying pressure medium to and/or draining pressure medium from the pressure chamber, a relative phase position of the output element in reference to the drive element and thus the camshaft in reference to the crankshaft can be variably adjusted For this purpose, pressure medium lines are provided, by which the pressure chamber, for example with a hydraulic control valve being interposed, can communicate with a pressure medium pump and a pressure medium reservoir of the internal combustion engine. 
     Alternatively, other embodiments of the phase adjustment device may also be provided, for example a phase adjustment device in an axially adjusting design, in which a piston, which can be axially displaced by pressure medium, cooperates via diagonal gears with the output element and the drive element. Such a phase adjustment device is known, for example, from DE 42 18 078 C1. 
     Additionally, a volume accumulator is provided comprising at least a housing and a separating element arranged inside said housing. The separating element may be embodied as a piston or a non-elastic diaphragm, and separates a supply chamber from a complementary chamber in the interior of the housing. Here, the supply chamber communicates with a pressure medium line, while the complementary chamber is ventilated, and for example communicates with the interior of the internal combustion engine. If the pressure medium line connected to the volume accumulator guides pressure medium the supply chamber fills and the separating element is displaced within the housing such that the volume of the supply chamber is enlarged and the volume of the complementary chamber accordingly reduced. Here, it may be provided that the complementary chamber comprises a ventilation opening, which communicates with the interior of the internal combustion engine. This way, gas can evaporate from the complementary chamber, for example into the crank housing or the cylinder head of the internal combustion engine so that no pressure develops in the complementary chamber. 
     When a piston is used as the separating element it is displaced during the filling of the supply chamber inside the housing. In case of a diaphragm it everts in the direction of the complementary chamber. 
     Due to the fact that no force accumulator is provided which is stressed during the filling process of the volume accumulator the filling occurs already at minimal operating pressures. Furthermore, the filled volume accumulator initially fails to empty under falling pressure into the pressure medium line. The supply chamber empties into the pressure medium line only when the pressure in the pressure medium line falls below the pressure existing in the complementary chamber, and thus for example within the crank housing. Thus, the entire volume of the volume accumulator of the phase adjustment device is only available from the moment of time at which the need for pressure medium is greater than the volume flow rate provided by the pressure medium pump. This way, alternating torques acting upon the camshaft can be used to a higher degree, which leads to considerably higher adjustment speeds. 
     When the internal combustion engine is turned off no forces impinge the separating element so that it is freely displaceable. During the operation of the internal combustion engine only one force impinges the surface of the separating element limiting the supply chamber, which is determined by the pressure existing in the pressure medium line communicating with the supply chamber. The area of the separating element limiting the complementary chamber is held essentially unaffected due to the ventilation. In particular, no force is applied to this area which increases with the fill level of the supply chamber, which is the case in pressure spring—volume accumulators. When the pressure in the pressure medium line communicating with the supply chamber exceeds the atmospheric pressure (=pressure in the chamber communicating with the complementary chamber) the volume accumulator is and/or remains filled. Only when the pressure in the pressure medium line falls below the atmospheric pressure the pressure medium is suctioned from the volume accumulator into the pressure medium line and is therefore available for the phase adjustment. Thus, the separating element is exclusively displaced by the pressure existing in the pressure medium line communicating with the volume accumulator. 
     In a more concrete design of the invention it is provided that the device furthermore comprises a control valve and at least one second pressure chamber, which acts against the first pressure chamber and that a first pressure medium line communicates with the control valve and the first pressure chamber such that a second pressure medium line communicates with the control valve and the second pressure chamber and that a third pressure medium line communicates with the control valve and the pressure medium pump, with the supply chamber communicating with the third pressure medium line. 
     In this embodiment a pressure chamber is provided inside the phase adjustment device, which is separated by a piston or a blade of an impeller into two oppositely acting pressure chambers. Each of the pressure chambers communicates via a pressure medium line with the operating connection of a control valve. Furthermore, another pressure medium line is provided, which connects the pressure medium pump with a supply connection of the control valve. The pressure medium pump can be optionally connected via the control valve to the first or the second pressure chamber. Simultaneously the other pressure chamber is connected to the pressure medium reservoir, so that the piston and/or the vane are displaced inside the pressure chamber. This motion is directly or indirectly transferred into an adjustment of the phase position of the output element in reference to the drive element. By the connection of the storage chamber to the pressure medium line connecting the pressure medium pump with the control valve the pressure medium is available both for adjustment processes in the direction of earlier as well as for adjustment processes in the direction of later control timing. Here, it is provided that the supply chamber is connected between the control valve and the pressure medium pump into the third pressure medium line. 
     Furthermore, it may be provided that one check valve is arranged upstream in the pressure medium line communicating with the supply chamber and one check valve downstream in reference to the volume accumulator, with both check valves preventing a reflux of pressure medium in the direction of the volume accumulator and/or the pressure medium pump. The check valves prevent that pressure medium from the pressure chambers to be filled, for example the pressure chambers connected to the supply connection of the control valve, can flow back into the volume accumulator or the pressure medium pump, when based on the alternating torques acting upon the camshaft pressure peaks develop in these pressure chambers. The pressure medium is therefore supported by the check valves, thus increasing the speed of the phase adjustment and preventing phase fluctuations. 
     The separating element can be embodied for example as a piston. Here, it may be embodied from plastic and additionally comprise reinforcement ribs. Alternatively the piston may also be embodied cup-shaped and made from a sheet-metal blank. Disk-shaped pistons are also possible. The piston can separate the supply chamber from the complementary chamber via play adjustment in the housing. Alternatively the piston may be provided with a sealing element, which cooperates with the housing in a sealing fashion. 
     In a further development of the invention it is provided that in the complementary chamber a limit stop is provided for the piston. The limit stop may be embodied in one piece with the housing or produced separately. Here it may be provided that the contact surface of the limit stop is embodied smaller than the area of the piston, which limits the complementary chamber. This way it is prevented that the piston engages the housing or the limit stop in a planar fashion, thus adhesion forces countering the emptying of the volume accumulator are reduced. The limit stop may be embodied surrounding a ventilation opening of the complementary chamber. Here, the limit stop may completely surround the ventilation opening or be embodied with one or more interruptions. 
     The volume accumulator may be arranged inside the internal combustion engine, for example. In this case, the gas and pressure medium may directly be ventilated from the complementary chamber into the interior of the internal combustion engine via a simple ventilation opening, additional seals are not necessary. Alternatively it may be provided that the volume accumulator is arranged outside the internal combustion engine, with a vent line being provided, which communicates on the one side with the complementary chamber and on the other side with the interior of the internal combustion engine. The vent line may be embodied in the housing of the volume accumulator or an additional housing, for example, encapsulating the volume accumulator. In this embodiment gaskets are provided, which seal the vent line and the connection between the supply chamber and the pressure medium line from the environment. 
     The volume accumulator may be connected, for example, via a thread embodied at the cylinder head, the crank housing, or another environmental construction. Advantageously the thread comprises an opening by which the supply chamber communicates with the pressure medium line. 
     In a more precise embodiment of the invention it is provided that the volume accumulator is arranged inside the camshaft. This way the volume accumulator can be integrated without increasing the space required for the internal combustion engine. Furthermore, this way a minimal distance is implemented between the volume accumulator and the phase adjustment device and thus the reaction behavior. Here, the interior wall of the camshaft serves as the housing in which the separating element is received. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features of the invention are discernible from the following description and the drawings, in which exemplary embodiments of the invention are shown in a simplified illustration. Shown are: 
         FIG. 1  an internal combustion engine, only schematically, 
         FIG. 2  a device according to the invention, with the phase adjustment device and the hydraulic circuit being shown schematically in a top view, 
         FIG. 3  a longitudinal cross-section through the phase adjustment device of  FIG. 2  along the line III-III, 
         FIG. 4  an view showing the alternating torque acting upon the camshaft, 
         FIG. 5  a first embodiment of a volume accumulator, 
         FIG. 6  a second embodiment of a volume accumulator, 
         FIG. 7  a third embodiment of a volume accumulator, and 
         FIG. 8  a fourth embodiment of the volume accumulator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  schematically shows an internal combustion engine  1 , with a piston  3  in a cylinder  4  located on a crankshaft  2  being indicated. In the embodiment shown, the crankshaft  2  is connected via one traction mechanism  5  each to an intake camshaft  6  and/or an exhaust camshaft  7 , with a first and a second device  11  ensuring a relative rotation between the crankshaft  2  and the camshafts  6 ,  7 . Cams  8  of the camshafts  6 ,  7 , operate one or more intake gas exchange valves  9  and/or one or more exhaust gas exchange valves  10 . Additionally it may be provided that only one of the camshafts  6 ,  7  is equipped with a device  11 , or only one camshaft  6 ,  7 , is provided which includes a device  11 . 
       FIGS. 2 and 3  show a first embodiment of a device  11  according to the invention, with a phase adjustment device  11   a  being shown in a top view and/or in a cross-section and the hydraulic circuit in a schematic fashion. The phase adjustment device  11   a  comprises a drive element  13  and an output element  14 . At each of the axial lateral surfaces of the drive element  13  a lateral cover  15  is fastened in a torque-proof fashion. The output element  14  is embodied in the form of an impeller and essentially comprises a cylindrically embodied hub element  16 , with in the embodiment shown five blades  17  extending from its exterior cylindrical casing in the radial direction outwardly. The blades  17  are embodied separated from the drive element  14  and arranged in blade grooves of the hub element  16 . The blades  16  are impinged radially outwardly with a force via torsion springs  18 , which are arranged between the base of the grooves of the blade grooves and the blades  17 . 
     Starting at an exterior circumferential wall  19  of the drive element  13  several projections  20  extend radially inwardly. In the embodiment shown the projections  20  are embodied in one piece with the circumferential wall. The drive element  13  is supported on the drive element  14 , rotational in reference thereto, via radially inwardly located circumferential walls of the projections  20 . 
     A sprocket  12  is arranged at an exterior casing surface of the drive element  13 , by which a torque can be transferred from the crankshaft  2  via a chain drive, not shown, to the drive element  13 . 
     Within the phase adjustment device  11   a , a pressure chamber  21  is embodied between each two adjacent projections  20  arranged in the circumferential direction. Each of the pressure chambers  21  is limited in the circumferential direction by opposite, essentially radially extending limiting walls  22  of neighboring projections  20 , in the axial direction by lateral covers  15 , radially inwardly by the hub element  16 , and radially outwardly by the circumferential wall  19 . A blade  17  projects into each of the pressure chambers  21 , with the blades  17  being embodied such that they contact both the lateral covers  15  as well as the circumferential wall  19 . Thus, each blade  17  divides the respective pressure chamber  21  into two pressure chambers  23 ,  24  acting opposite each other. 
     The output element  14  is received in the drive element  13  and supported in a rotary fashion thereto over a defined angular range. The angular range is limited in the rotary direction of the drive element  14  such that the blades  17  contact one a corresponding limiting wall  22  each (early stop  22   a ) of the pressure chambers  21 . Similarly, the angular range is limited in the other direction such that the blades  17  contact the other limiting walls  22  of the pressure chambers  21 , which serve as the late stop  22   b.    
     By impinging a group of pressure chambers  23 ,  24  with pressure and releasing the pressure of the other group the phase position of the drive element  14  can be varied in reference to the drive element  13 . By impinging both groups of pressure chambers  23 ,  24  with pressure the phase position can be held constant. Alternatively it may be provided that the pressure chambers  23 ,  24  during the phases of constant phase position are impinged with pressure medium. Usually the oil of the internal combustion engine  1  is used as the hydraulic pressure medium. 
     A hydraulic circuit  25  is provided for the supply with pressure medium and/or the draining of pressure medium from the pressure chambers  23 ,  24 , which comprises a pressure medium pump  26 , a pressure medium reservoir  27 , a control valve  28 , and several pressure medium lines  25   a,b,p . The control valve  28  comprises an inlet connection P, a tank connection T, and two operating connections A, B. The first pressure medium line  25   a  connects the first operating connection A with the first pressure chambers  23 . The second pressure medium line  25   b  connects the second operating connection B with the second pressure chambers  24 . The third pressure medium line  25   p  connects the pressure medium pump  26  with the inlet connection P. 
     Pressure medium transported by the pressure medium pump  26  is supplied via the third pressure medium line  25   p  to the inlet connection P of the control valve  28 . Depending on the control status of the control valve  28 , the inlet connection P is connected to the first pressure medium line  25   a , the second pressure medium line  25   b , or both and/or none of the pressure medium lines  25   a,b.    
     In order to shift the control timing (opening and closing time) of the gas exchange valves  9 ,  10  in the early direction the pressure medium supplied to control valve  28  via the third pressure medium line  25   p  is guided via the first pressure medium line  25   a  to the first pressure chambers  23 . Simultaneously, the pressure medium from the second pressure chambers  24  reaches via the second pressure medium line  25   b  the control valve  28  and is ejected into the pressure medium reservoir  27 . This way the blades  17  are shifted in the direction of the early stop  22   a , thus a rotary motion of the output element  14  is achieved in reference to the drive element  13  in the rotary direction of the phase adjustment device  11   a.    
     In order to shift the control timing of the gas exchange valve  9 ,  10  in the late direction, the pressure medium supplied to the control valve  28  via the third pressure medium line  25   p  is guided via the second pressure medium line  25   b  to the second pressure chambers  24 . Simultaneously pressure medium from the first pressure chambers  23  reaches via the first pressure medium line  25   a  the control valve  28  and is ejected into the pressure medium reservoir  27 . This way the blades  17  are shifted in the direction towards the late stop  22   b , thus leading to a rotary motion of the output element  14  in reference to the drive element  13  against the rotary direction of the phase adjustment device  11   a.    
     In order to hold the control timing constant the supply of pressure medium is either prevented or permitted to all pressure chambers  23 ,  24 . This way, the blades  17  inside the respective pressure chambers  21  are hydraulically clamped and any rotary motion of the output element  14  in reference to the drive element  13  is prevented. 
     During the operation of the internal combustion engine  1 , the camshaft  6 ,  7  rotates about its longitudinal axis. Here, each gas exchange valve  9 ,  10  is periodically opened against the force of a valve spring  30  and closed again. During the open phase of the gas exchange valve  9 ,  10  (approaching cam) a braking torque is applied upon the camshaft  6 ,  7 , which is equivalent to the vector product of the force of the valve spring  30  with the lever of the cam  8 . During the closing of the gas exchange valve  9 ,  10  (removing cam) an accelerating torque acts upon the camshaft  6 ,  7 , which is equivalent to the vector product of the force of the valve spring  30  with the lever of the cam  8 . In this way, a periodic, alternating torque M acts upon the camshaft  6 ,  7 , which is shown in  FIG. 4  applied over the crankshaft angle α. 
     During a phase shift in the direction of later (earlier) control timing the positive (negative) portion of the alternating torque M, shown in  FIG. 4 , supports the phase shift. Here, the output element  14  is adjusted both by the system pressure provided by the pressure medium pump  26  as well as by the positive (negative) portion of the alternating torque M towards earlier (later) control timing and thus the speed of the phase adjustment is increased. In internal combustion engines  1  with high alternating torque M this may lead to the adjustment process induced by the alternating torque M occurring with such a high speed that the volume of pressure medium transported by the pressure medium pump  26  is insufficient to properly supply the expanding second (first) pressure chambers  24 , ( 23 ) with pressure medium. As a consequence, in the second (first) and third pressure medium line  25   b  ( a ),  p  a vacuum develops which counteracts the adjustment process. Thus, the alternating torques M acting upon the camshaft  6 ,  7  cannot be optimally utilized, and instead they act only up to a limit torque M 1 . 
     Simultaneously the negative (positive) portion of the alternating torque M acts against the phase adjustment. When the negative (positive) portion of the alternating torque M exceeds the torque generated by the pressure medium pump  26  the pressure medium is removed from the second (first) pressure chambers  24  ( 23 ) into the second (first) and third pressure medium line  25   b  ( a ),  p  and a brief phase adjustment occurs opposite the desired direction. 
     In order to prevent these effects, the pressure medium pump  26  can be sized appropriately bigger, thus the installation space required, the costs, and the fuel consumption of the internal combustion engine  1  are increased. 
     Alternatively, according to the invention a volume accumulator  31  can be provided.  FIG. 5  shows a potential embodiment of a volume accumulator  31 , which is arranged inside the internal combustion engine  1 . It comprises a housing  32 , in which a separating element  33  is arranged that is free floating and can be freely shifted. The separating element  33  is embodied as a piston in the embodiment shown, which divides the housing  32  into a supply chamber  34  and a complementary chamber  35 . Here, the piston carries a sealing element  38 , which seals the two chambers from each other. The supply chamber  34  connects to the third pressure medium line  25   p  between two (optional) check valves  29 . The complementary chamber  35  communicates via the ventilation opening  36  with the interior of the internal combustion engine  1 . 
     When the pressure in the third pressure medium line  25   p  exceeds the pressure existing in the interior of the internal combustion engine  1 , the piston is shifted by the pressure medium flowing in the housing  32  in the direction of the limit stop  37 . This way the volume of the storage chamber  34  increases at the expense of the volume of the complementary chamber  35  until the piston contacts the limit stop  37  ( FIG. 5 , upper illustration of the volume accumulator  31 ). Simultaneously the gas present in the complementary chamber  35  can evacuate via the ventilation opening  35  into the interior of the internal combustion engine  1 . 
     Different from pressure springs or gas accumulators known from prior art here no force accumulator is provided, for example a pressure spring or a compressible gas cushion, which during the filling process is stressed. Here the volume accumulator  31  is arranged such that the displacement path of the separating element  33  extends perpendicular in reference to gravity. This way, gravity is not effective in the direction of displacement of the separating element  33 , thus the volume storage  31  is not emptied during down-times of the internal combustion engine, either. 
     The volume accumulator  31  reaches its completely filled state already at low system pressures. Furthermore, no automatic emptying of the volume accumulator  31  occurs during falling system pressure in the third pressure medium line  25   p , as long as the pressure is greater or equal to the pressure existing inside the internal combustion engine  1 . 
     When an alternating torque M acts upon the camshaft  6 ,  7  supporting the phase adjustment the pressure medium is suctioned from the first and/or second pressure medium line and the third pressure medium line  25   a,b,p  into the expanding pressure chambers  23 ,  24 , thus lowering the pressure in these pressure medium lines  25   a, b, p  below the pressure existing inside the internal combustion chamber  1 . Consequently the volume of pressure medium stored in the supply chamber  34  is suctioned into the third pressure medium line  25   p  and further transported to the respective pressure chambers  23 ,  24 . Here, the piston is shifted inside the housing  32  in the direction of the outlet opening of the supply chamber  34  ( FIG. 5 , lower illustration of the volume accumulator  31 ). Thus the phase adjustment device  11   a  provides an additional pressure medium volume, which is only mobilized when the volume of pressure medium transported by the pressure medium pump  26  is lower than the volume of pressure medium required for the phase adjustment induced by the alternating torque M. This way, the maximally utilized limit torque M 2  and thus the phase adjustment speed is significantly increased. 
     When the alternating torque M acting upon the camshaft  6 ,  7  against the phase adjustment direction the check valves  29  prevent pressure medium from the pressure chambers  23 ,  24  from being pushed into the volume accumulator  31  and/or in the hydraulic circuit  25 ; the pressure medium is supported by the check valve  29 . 
     This way the supporting portion of the alternating torque M is used to a higher degree for increasing the speed of phase adjustment and the opposite acting portion is compensated. Here, the emptying of the volume accumulator  31 , due to the freely displaceable piston (i.e. the lack of a force accumulator), only begins when the volume of pressure medium transported by the pressure medium pump  26  is smaller than the volume of pressure medium required. 
     In this embodiment the piston is embodied as a cylindrical part and may comprise a metallic material or a suitable plastic. The limit stop  37  surrounds the ventilation opening  36 , with its surface facing the piston being embodied smaller than the piston area in order to reduce adhesion forces. 
       FIG. 6  shows a second embodiment of a volume accumulator  31  of a device  11  according to the invention. Contrary to the first embodiment the piston is embodied cup-shaped and made from sheet metal in a deep-drawing process. The sealing of the supply chamber  34  from the complementary chamber  35  occurs via a narrowly tolerated sealing gap between the exterior jacket surface of the piston and the interior jacket surface of the housing  32 . The limit stop  37  is embodied in one piece with the housing  32 . Also possible are embodiments in which the limit stop  37  is made as a separate part and fastened in the housing  32 . Here, the separate limit stop  37  may be embodied as an O-ring, thus increasing the sealing effect between the piston and the housing  32  when the volume accumulator  31  is completely filled. 
     The housing  32  comprises a pin  40  with a penetrating bore, which opens on the one side in the supply chamber  34  and on the other side in the third pressure medium line  25   p . Using a thread formed at the exterior casing surface of the pin  40 , the housing  32  is fastened to an environmental construction  42 , for example a cylinder head or a crank housing. 
       FIG. 7  shows a third embodiment of a volume accumulator  31  of a device  11  according to the invention. Contrary to the first embodiment the limit stop  37  is interrupted in the circumferential direction by recesses  39 , thus reducing the contact area between the piston and the limit stop  37  and also the adhesion forces acting between these parts. In this embodiment the piston is made from a suitable plastic and may be provided with reinforcement ribs. 
       FIG. 8  shows a fourth embodiment of the volume accumulator  31  of a device  11  according to the invention. Contrary to the previous embodiments this volume accumulator  31  is arranged outside the internal combustion engine  1 . The housing  32  comprises a pin  40  with a penetrating bore, which in turn opens on one side in the supply chamber  34  and on the other side in the third pressure medium line  25   p . The housing  32  is capped by a second housing  41 , which is fastened by a screw connection to the cylinder head  42 . Within the second housing  41  a ventilation line  43  is formed, by which the complementary chamber  35  communicates with the interior of the internal combustion engine  1 . Thus, gas and pressure medium can be guided from the complementary chamber  35  into the interior of the internal combustion engine  1  when the piston is moved in the direction towards the limit stop  37 . At the contact area between the cylinder head  42  and the first and/or second housing  31 ,  41 , sealing rings  44  are provided in order to prevent the emission of pressure medium. Embodiments are also possible in which only a thick-walled housing  31  is provided in which the ventilation line  43  is embodied. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Internal combustion engine 
           2  Crankshaft 
           3  Piston 
           4  Cylinder 
           5  Traction mechanism 
           6  Inlet camshaft 
           7  Outlet camshaft 
           8  Cam 
           9  Inlet gas exchange valve 
           10  Outlet gas exchange valve 
           11  Device 
           11   a  Phase adjustment device 
           12  Sprocket 
           13  Drive element 
           14  Output element 
           15  Lateral cover 
           16  Hub element 
           17  Blade 
           18  Torsion spring 
           19  Circumferential wall 
           20  Projection 
           21  Pressure chamber 
           22  Limiting wall 
           22   a  Early stop 
           22   b  Late stop 
           23  First pressure chamber 
           24  Second pressure chamber 
           25  Hydraulic circuit 
           25   a  First pressure medium line 
           25   b  Second pressure medium line 
           25   p  Third pressure medium line 
           26  Pressure medium pump 
           27  Pressure medium pump 
           28  Control valve 
           29  Check valve 
           30  Valve spring 
           31  Volume accumulator 
           32  Housing 
           33  Separating element 
           34  Supply chamber 
           35  Complementary chamber 
           36  Ventilation opening 
           37  Limit stop 
           38  Sealing element 
           29  Recess 
           40  Pin 
           41  Second housing 
           42  Environmental structure 
           43  Ventilation line 
           44  Gasket 
         A First operating connection 
         B Second operating connection 
         P Inlet connection 
         T Outlet connection 
         α Crankshaft angle 
         M Alternating torque 
         M 1 , M 2  Limit torque