Abstract:
A directional control valve ( 2 ) for controlling a flow of hydraulic oil from a pressure connection ( 80 ) via work chambers of a camshaft adjuster ( 90 ) to a tank connection ( 88 ). The disclosed directional control valve ( 2 ) includes an accumulator connection ( 86 ) for guiding at least a part of the hydraulic oil flowing out from a work chamber into a volume accumulator ( 126 ) before the discharge into the tank connection ( 88 ).

Description:
INCORPORATION BY REFERENCE 
       [0001]    The following documents are incorporated herein by reference as if fully set forth: German Patent Application No. 10 2012 201 567.1, filed Feb. 2, 2012. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a directional control valve for controlling a flow of hydraulic oil from a pressure connection via work chambers of a camshaft adjuster to a tank connection and also relates to the camshaft adjuster. 
       BACKGROUND 
       [0003]    Camshaft adjusters are technical assemblies for adjusting the phase positions between a crankshaft and a camshaft in an internal combustion engine. 
         [0004]    From DE 10 2010 012 479 A1, it is known to control the flow of hydraulic oil by a directional control valve that is screwed centrally into the camshaft and thus simultaneously fixes the rotor of the camshaft adjuster on the camshaft. 
       SUMMARY 
       [0005]    The objective of the invention is to improve the known directional control valve. 
         [0006]    This objective is met by one or more features of the invention. Preferred refinements are described below and in the claims. 
         [0007]    The invention provides the integration a connection for a volume accumulator of the camshaft adjuster in the directional control valve. 
         [0008]    This is based on the idea that a volume accumulator that is connected to the pressure chambers of the camshaft adjuster can be integrated into the camshaft adjuster. If there is an under-pressure of hydraulic oil in the pressure chambers, then this can be equalized by the volume accumulator. An equalization of an over-pressure usually present relative to the volume accumulator can be prevented by a non-return valve. 
         [0009]    Forming the basis of this idea is the concept of the invention to supply the volume accumulator with the hydraulic oil that flows out from the pressure chambers of the camshaft adjuster. For this purpose, the oil flowing out from the pressure chambers is not guided to the tank connection but instead to an accumulator connection by which the volume accumulator can be filled with oil. Only after the hydraulic oil has passed the volume accumulator does it flow out via the tank connection. 
         [0010]    The invention therefore discloses a directional control valve for controlling a flow of hydraulic oil from a pressure connection via work chambers of a camshaft adjuster to a tank connection that comprises an accumulator connection for guiding at least one part of the hydraulic oil flowing out from a work chamber into a volume accumulator before the discharge into the tank connection. 
         [0011]    In one refinement of the invention, the disclosed directional control valve comprises a control piston and a central screw in which the control piston is held. Here, the central screw has a screw shaft and a screw head set on the screw shaft in the axial direction. Through the central screw, the directional control valve can be used not only for controlling the flow of hydraulic oil but also for mounting components of the camshaft adjuster, for example, a rotor. 
         [0012]    In an additional refinement of the invention, the accumulator connection comprises a radial hole through the screw shaft of the central screw. The radial hole can be arranged in an axial plane of the screw shaft that is different from an axial plane of the screw shaft in which the work connections or the pressure connection is formed. In this way it is possible to screw the central valve in the camshaft adjuster without orientation, because a peripheral groove can be formed around the radial hole of the accumulator connection, with this groove leading the hydraulic oil into the radial hole from any angular position. 
         [0013]    In an alternative or additional refinement of the invention, the accumulator connection comprises a radial hole through the screw head of the central screw. This can be formed as an alternative to or in addition to the radial hole through the screw shaft and can be subjected to the same technical criteria as the radial hole through the screw shaft. 
         [0014]    In one special refinement of the invention, the radial hole through the screw shaft is formed in a common axial plane with a connection for supplying the work chambers of the camshaft adjuster with the hydraulic oil. In this way, the central valve and thus also the corresponding components of the camshaft adjuster that sit on the central valve can be formed in an especially space-saving way in the axial direction. Forming the radial hole for the accumulator connection in a common axial plane with the work connections of the camshaft adjuster is especially suitable when the central valve can be screwed oriented in a certain angular position in the camshaft adjuster and the radial hole through the central valve can be set with an accurate fit on a corresponding connection on the rotor or stator that leads the hydraulic oil into one of the pressure chambers of the camshaft adjuster. 
         [0015]    In one especially preferred refinement of the invention, the control piston projects past the screw head in the axial direction, wherein the accumulator connection is formed in the axial projecting region of the control piston. In this way, the components of the camshaft adjuster forming the pressure chambers do not have to be widened further in the axial direction, in order to also have the radial hole for the accumulator connection. In addition, the smallest hydraulic resistance and thus losses occur when the hydraulic oil is discharged via the region projecting in the axial direction. 
         [0016]    The invention also discloses a camshaft adjuster that comprises a stator for storing rotational energy from a crankshaft of an internal combustion engine, a rotor mounted so that it can rotate in the stator for discharging the rotational energy to a camshaft for controlling the internal combustion engine, and a disclosed directional control valve that can be screwed into the camshaft in the axial direction for mounting the rotor on the camshaft. 
         [0017]    In one refinement of the invention, the rotor has a peripheral groove on its inner radial side directed toward the directional control valve in an axial plane intersecting the accumulator connection. Through the peripheral groove, the accumulator connection on the directional control valve is connected to an accumulator connection on the rotor when the directional control valve is inserted in an undefined angular position in the camshaft adjuster. 
         [0018]    In another refinement of the invention, the rotor is stepped outward in the radial direction. In this way, for installing the accumulator connection in the disclosed camshaft adjuster, only a region lying lower in the radial direction must be widened in the axial direction, while the radial outer region of the rotor and thus the radial outer region of the stator in which, for example, the cover screws of the camshaft adjuster can be arranged can be held to their original axial length. 
         [0019]    In one special refinement of the invention, the stator comprises an axial cover for closing a chamber holding the rotor, wherein the axial cover has an axial chamfer that is oriented, viewed from an axis of rotation, toward the rotor. Through the chamfer the axial cover can collect hydraulic oil from the central valve and forward it to the rotor via the centrifugal forces when camshaft adjuster is operating. In this way, the volume accumulator can be formed in the rotor, wherein the axial cover can be used as a supply line of the volume accumulator. 
         [0020]    In one especially preferred refinement of the invention, the axial cover comprises a passage for an actuator moving the control piston and a seal for sealing a radial gap between the passage and the actuator. In this way, losses of hydraulic oil can be kept small on the axial end side of the camshaft adjuster. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of the invention are explained below in more detail with reference to a drawing in which: 
           [0022]      FIGS. 1A and 1B  are two views of a central valve in a first position, 
           [0023]      FIGS. 2A and 2B  are views of the central valve in a second position, 
           [0024]      FIG. 3  is a section view of a camshaft adjuster with the central valve of  FIGS. 1 and 2 , 
           [0025]      FIG. 4  is a section view of another central valve, 
           [0026]      FIG. 5  is a section view of a camshaft adjuster with the central valve of  FIG. 4 , and 
           [0027]      FIG. 6  is a section view of another central valve. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    In the figures, identical elements are provided with identical reference symbols and are described only once. 
         [0029]    Reference will be made to FIGS.  1 A, 1 B and  2 A,  2 B. In  FIGS. 1A ,  1 B and  2 A,  2 B, a central valve  2  is shown in a two projection view. While  FIG. 1B  shows a section view of the central valve  2  in a first position,  FIG. 2B  shows a section view of the central valve  2  in a second position that is rotated by 45° relative to the first position. The central valve  2  has a rotationally symmetric construction about an axis of rotation  3 . Some elements of the central valve  2  are shown in different axial positions for better illustration of the circumstances in the section views of the central valve  22 . 
         [0030]    The central valve  2  has a central screw  4 , a valve housing  6 , a control piston  8 , a non-return valve  10 , a spring  12 , and a retaining ring  14 . 
         [0031]    The central screw  4  has a screw head  16 , a screw shaft  18 , and an inner space  20 . The screw shaft  18  is adjacent to the screw head  16 . On its axial end opposite the screw head  16 , an eternal thread  22  is formed that can be screwed into a corresponding nut thread, for example, in a camshaft still to be described. Viewed in the axial direction from the screw shaft  22 , first radial central screw holes  24  are formed in a first axial plane of the central screw  4 , second radial central screw holes  26  are formed in a second axial plane, third radial central screw holes  28  are formed in a third axial plane, fourth radial central screw holes  30  are formed in a fourth radial plane, and fifth radial central screw holes  31  are formed in a fifth radial plane. An axial central screw opening  32  is guided through the screw head  16  of the central screw  4 . The radial central screw holes  24  to  30  and the axial central screw opening  32  open the inner space  20  of the central screw  4  to the outside. The screw head  16  also has a hexagonal area  34  in which a corresponding hexagonal wrench can engage, in order to exert a torque on the central screw. 
         [0032]    The non-return valve  10  is held in the inner space  20  of the central screw  4 . It is inserted via the axial central screw opening  32  up to an axial end of the inner space  20  of the central screw  4  that lies opposite the axial central screw opening  32 . The non-return valve  10  has a hollow cylinder  36  in which a peripheral non-return valve groove  38  is formed. In the non-return valve groove  38 , radial non-return valve holes  40  are guided through the hollow cylinder  36 . The non-return valve groove  38  lies in the same axial plane in which the first central screw holes  24  lie, so that the non-return valve groove  38  is opened via the first central screw holes  24  to the outside. A ball cage  42  is adjacent to the hollow cylinder  36  in the axial direction. The ball cage  42  has, on its side directed toward the hollow cylinder  36 , an axial ball cage opening  44  that contacts a ball  46 . The ball is supported on the side opposite the ball cage opening  44  in a ball cage inner space  48  with a spring that is not described in more detail and that presses the ball  46  into the ball cage opening  44 . The ball cage inner space  48  is opened via radial ball cage holes  50  to the outside. 
         [0033]    In the inner space  20  of the central screw  4 , the valve housing  6  is set on the non-return valve  10  in the axial direction. It has first radial valve housing holes  52 , second radial valve housing holes  54 , third radial valve housing holes  56 , fourth radial valve housing holes  57 , fifth radial valve housing holes  58 , and sixth radial valve housing holes  59 . The valve housing  6  also has first axial valve housing grooves  60 , second axial valve housing grooves  61 , and third axial valve housing grooves  62 . Of these elements, only one of each is provided with a reference symbol in  FIGS. 1 and 2  for the sake of clarity. While the first radial valve housing holes  52  are arranged in the second axial plane of the second radial central screw holes  26  and the sixth radial valve housing holes  59  are arranged in the fifth axial plane of the fifth central screw holes  31 , the second radial valve housing holes  54  are arranged in an axial plane between the third axial plane of the third radial central screw holes  28  and the fourth axial plane of the fourth radial central screw holes  30  and the third radial valve housing holes  56  in an axial plane between the fourth axial plane of the fourth radial central screw holes  30  and the fifth axial plane of the fifth radial central screw holes  31 . The second radial valve housing holes  54  are connected via the first axial valve housing grooves  60  to the third radial central screw holes  28 , while the third radial valve housing holes  56  are connected via the second axial valve housing grooves  61  to the fourth radial central screw holes  28 . Finally, the third axial valve housing groove  62  connects the fourth and fifth radial valve housing holes  57 ,  58  to each other. 
         [0034]    In the interior of the valve housing  6 , the control piston  8  is held so that it can move in the axial direction. The control piston  8  is supported in the axial direction against the ball cage  42  with the spring  12 , so that a spring space  64  is formed between the ball cage  42  and the control piston  8 . The control piston  8  is also closed relative to the spring  12  in the axial direction by a wall  66 , so that there can be no exchange of hydraulic fluid between a control piston space  68  and the spring space  64 . On the control piston  8  there are also a first peripheral control piston groove  70 , a second peripheral control piston groove  72 , and a third peripheral control piston groove  74 . The first peripheral control piston groove  70  is opened into the control piston space  68  by means of first radial control piston holes  76 , while the third peripheral control piston groove  74  is opened into the control piston space  68  by second radial control piston holes  78 . The second peripheral control piston groove  72  is not opened into the control piston space  68 . 
         [0035]    The control piston  8  can be moved from a first axial position to a second axial position, for example, by means of a not-shown central magnet that can contact an axial end of the control piston  8  opposite the spring  12 . The spring  12  then pushes the control piston  8  from the second axial position back into the first axial position. In  FIGS. 1B and 2B , the first axial position of the control piston  8  is shown above the axis of rotation  3 , while the second axial position of the control piston  8  is shown below the axis of rotation  3 . 
         [0036]    During the operation of the central valve  2 , the control piston  8  is moved back and forth for the operation of the camshaft adjuster, in order to fill and empty the pressure chambers of the camshaft adjuster with hydraulic fluid. 
         [0037]    By use of a pressure connection  80 , a pressurized hydraulic oil can be fed to the central valve  2  by the first central screw hole  24 , flowing via the peripheral hollow cylinder groove  38  and the radial hollow cylinder hole  40  into the non-return valve  10 . There the oil presses the ball  46  into the ball cage  42  and flows via the radial ball cage holes  50  via the third axial valve housing grooves  62  into the second peripheral control piston groove  72 . In this way, the second control piston groove  72  is always supplied with hydraulic oil from the pressure connection  80  regardless of its position. 
         [0038]    In the first axial position of the control piston  8 , the second control piston groove  72  lies above the third radial valve housing hole  56  in the axial direction. In this way, a first work connection  82  leading to a first pressure chamber of the camshaft adjuster is supplied with the hydraulic oil from the pressure connection  80  of the camshaft adjuster via the fourth radial central screw hole  30 . In a way known to someone skilled in the art, a second pressure chamber of the camshaft adjuster discharges hydraulic oil accordingly to a second work connection  84 . This discharged hydraulic oil is led via the third radial central screw holes  28  and the first axial valve housing grooves  60  to the second radial valve housing holes  54 . At the second radial valve housing holes  54 , the axial first peripheral control piston groove  70  holds the hydraulic oil flowing out of the second pressure chamber and leads it via the second radial control piston holes  78  into the control piston space  68 . From this space the hydraulic oil flows via the first radial control piston holes  76  into the third peripheral control piston groove  74  into the sixth radial valve housing hole  59  and thus the fifth radial central screw hole  31 . At this fifth radial central screw hole  31 , there is a volume accumulator connection  86  that leads the hydraulic oil into a volume accumulator of the camshaft adjuster that is provided for equalizing under-pressures in the pressure chambers of the camshaft adjuster. 
         [0039]    In the second axial position of the control piston  8 , the second control piston groove  72  lies with the hydraulic oil from the pressure connection  80  in the axial direction above the second radial valve housing hole  54 , so that the second work connection  84  is provided with hydraulic oil and the hydraulic oil is pressed out of the first work connection  82 . In the second axial position of the control piston  8 , the third peripheral control piston groove  74  lies simultaneously in the axial direction above the third radial valve housing hole  56  and the sixth radial valve housing hole  59 , so that the hydraulic oil is led from the first work connection  82  directly via the third peripheral control piston groove  74  into the volume accumulator connection  86 . 
         [0040]    For venting the spring space  64 , a tank connection  88  can also be provided that vents the spring space  64  via the first radial valve housing hole  52  and the second radial central screw hole  26 . 
         [0041]    In the present construction, the hydraulic oil is led through the screw shaft to the volume accumulator connection  86  of the central screw. 
         [0042]    Forwarding the hydraulic oil into the volume accumulator is explained in more detail with reference to  FIG. 3  that shows a section view of a camshaft adjuster  90  with the central valve  2  of  FIGS. 1B and 2B . In  FIG. 3 , some elements of the central valve  2  that were already described in  FIGS. 1A ,  1 B and  2 A,  2 B are no longer provided with reference symbols. 
         [0043]    In addition to the central valve  2 , the camshaft adjuster  90  has a rotor  92  set on the central valve  2  in the axial direction, a stator  94  in which the rotor  92  is held, a front cover  96  set on the stator  94  in the axial direction, a back cover  98  set on the stator  94  in the axial direction, screws  100  for screwing the cover  96 ,  98  on the stator  94 , a spiral spring  102  clamped between the rotor  92  and the stator  94 , and a spring cover  104  covering the spiral spring  102 . 
         [0044]    The rotor  92  is held in the stator  94  in the axial direction. The front cover  96  and the back cover  98  are set on the stator  94  in the axial direction and screwed on with the screws  100 . Together with the stator  94 , the rotor  92  forms the pressure chambers that were already mentioned in the scope of  FIGS. 1 and 2  in a way known to someone skilled in the art. 
         [0045]    One of the two screws  100  shown in  FIG. 3  has an axial extension  106  on its tip in which the spiral spring  102  is suspended on the stator side. On the rotor side, the spiral spring  102  can be suspended on slots that are not shown in more detail. The back cover  98  also has a peripheral slot  108  in which the spring cover  104  is clamped in the radial direction. 
         [0046]    The stator  94  also has, on its periphery, teeth  110  in which a driving means, for example, a chain, driven by a not-shown crankshaft of an internal combustion engine can engage, in order to turn the stator  94 . The rotor  92  is clamped in the axial direction between the screw head  16  of the central screw  4  and a camshaft  112  and is thus connected rigidly to the camshaft. In this way, the rotational energy received from the stator  94  is transmitted from the crankshaft via the rotor  92  to the camshaft  112 . 
         [0047]    For clamping the rotor  92  between the screw head  16  and the camshaft  112 , the camshaft  112  has an axial inner space  114  that is opened toward the camshaft adjuster  90  and on whose end an internal thread  116  is formed. The external thread  22  of the central screw  4  is screwed into this internal thread  116 , so that the rotor  92  can be clamped rigidly between the screw head  16  and the camshaft  112 . 
         [0048]    Hydraulic oil can be filled into the inner space  114  via a radial hole  118  through the camshaft  112  and led to the pressure connection  80 . On a side of the rotor  92  directed toward the central valve  2 , a first peripheral groove  120 , a second peripheral groove  122 , and a third peripheral groove  124  are formed. The first and second peripheral grooves  120 ,  122  lie on the first and second work connection  82 ,  84  in the radial direction accordingly and distribute the hydraulic oil flowing to the pressure chambers or from the pressure chambers in the peripheral direction around the central screw  4 , so that the hydraulic oil can always flow out from or into the corresponding radial central screw holes  28 ,  30  regardless of the angular position of the central screw  4  relative to the rotor  92 . 
         [0049]    In the same way, the third peripheral groove  124  contacts, in a not-shown way, the volume accumulator connection  84 . From the third peripheral groove  124 , a radial hole not shown in  FIG. 3  leads through the rotor  92  into a volume accumulator  126  that is formed between the rotor  92  and the front cover  96  and provides the under-pressure compensation in the pressure chambers of the camshaft adjuster  90 . Excess hydraulic oil is guided from the volume accumulator  126  via an outlet  128  from the camshaft adjuster  90  to which the tank connection  86  of the central valve  2  is also connected. 
         [0050]    In the present construction, the rotor  92  is stepped in the radial direction. The front cover  96  is set on the rotor  92  inclined relative to this rotor in the radial direction. In this way, the hydraulic fluid in the volume accumulator  126  slides during the operation of the camshaft adjuster  90 , when this is turning, due to the centrifugal forces acting on the hydraulic fluid and the shape of the front cover  96  to the automatic rotor  92 . 
         [0051]    In  FIG. 4 , a section view of another central valve  2  is shown, while in  FIG. 5  a section view of a camshaft adjuster  90  with the central valve  2  of  FIG. 4  is shown. The position of the central valve  2  in  FIG. 4  corresponds to the position of the central valve  2  in  FIG. 2B . 
         [0052]    In the construction of  FIGS. 4 and 5 , the fifth radial central screw hole  31  is guided through the screw head  16  of the central screw  4 . In this way, the rotor  92  can have a shorter axial construction. The volume accumulator  126  is bounded in the present construction by the screw head  16 , the rotor  92 , and the front cover  96 . 
         [0053]    In  FIG. 5 , a central magnet  130  is also shown for the axial movement of the control piston  8  in the way named above, as well as non-return valves  132  in the volume accumulator  126  for supplying the pressure chambers with hydraulic oil in the event of an under-pressure. 
         [0054]    In  FIG. 6 , a section view of a camshaft adjuster  90  with a modified central valve  2  of  FIG. 4  is shown. The position of the central valve  2  in  FIG. 6  corresponds to the position of the central valve  2  in  FIG. 1B . 
         [0055]    In  FIG. 6 , the volume accumulator connection  86  is formed in the axial head of the control piston  8 . The hydraulic oil flowing from the pressure chambers via the work connections  82 ,  84  flows via this volume accumulator connection  86  into the front cover  96 , wherein the hydraulic oil is led, as in the previous embodiments, by the centrifugal force generated during the operation of the camshaft adjuster  90  to the rotor  92  and the corresponding non-return valves  132  to the pressure chambers. 
         [0056]    A gap  134  between a passage through the front cover  96  and a tappet  136  of the central magnet  130  should be sealed in this way, in order to keep any oil loss as low as possible. 
       LIST OF REFERENCE NUMBERS 
       [0057]      2  Central valve 
         [0058]      3  Axis of rotation 
         [0059]      4  Central screw 
         [0060]      6  Valve housing 
         [0061]      8  Control piston 
         [0062]      10  Non-return valve 
         [0063]      12  Spring 
         [0064]      14  Retaining ring 
         [0065]      16  Screw head 
         [0066]      18  Screw shaft 
         [0067]      20  Inner space 
         [0068]      22  Outer thread 
         [0069]      24  Radial central screw hole 
         [0070]      26  Radial central screw hole 
         [0071]      28  Radial central screw hole 
         [0072]      30  Radial central screw hole 
         [0073]      31  Radial central screw hole 
         [0074]      32  Axial central screw opening 
         [0075]      34  Hexagonal area 
         [0076]      36  Hollow cylinder 
         [0077]      38  Peripheral non-return valve groove 
         [0078]      40  Radial non-return valve hole 
         [0079]      42  Ball cage 
         [0080]      44  Ball cage opening 
         [0081]      46  Ball 
         [0082]      48  Ball cage inner space 
         [0083]      50  Radial ball cage hole 
         [0084]      52  Radial valve housing hole 
         [0085]      54  Radial valve housing hole 
         [0086]      56  Radial valve housing hole 
         [0087]      57  Radial valve housing hole 
         [0088]      58  Radial valve housing hole 
         [0089]      59  Radial valve housing hole 
         [0090]      60  Axial valve housing groove 
         [0091]      61  Axial valve housing groove 
         [0092]      62  Axial valve housing groove 
         [0093]      64  Spring space 
         [0094]      66  Wall 
         [0095]      68  Control piston space 
         [0096]      70  Control piston groove 
         [0097]      72  Control piston groove 
         [0098]      74  Control piston groove 
         [0099]      76  Radial control piston hole 
         [0100]      78  Radial control piston hole 
         [0101]      80  Pressure connection 
         [0102]      82  Work connection 
         [0103]      84  Work connection 
         [0104]      86  Volume accumulator connection 
         [0105]      88  Tank connection 
         [0106]      90  Camshaft adjuster 
         [0107]      92  Rotor 
         [0108]      94  Stator 
         [0109]      96  Front cover 
         [0110]      98  Back cover 
         [0111]      100  Screw 
         [0112]      102  Spiral spring 
         [0113]      104  Spring cover 
         [0114]      106  Axial extension 
         [0115]      108  Peripheral slot 
         [0116]      110  Teeth 
         [0117]      112  Camshaft 
         [0118]      114  Inner space of the camshaft 
         [0119]      116  Inner thread 
         [0120]      118  Radial hole through the camshaft 
         [0121]      120  Peripheral groove on the rotor 
         [0122]      122  Peripheral groove on the rotor 
         [0123]      124  Peripheral groove on the rotor 
         [0124]      126  Volume accumulator 
         [0125]      128  Outlet for tank connection 
         [0126]      130  Central magnet 
         [0127]      132  Non-return valve 
         [0128]      134  Gap 
         [0129]      136  Tappet