Abstract:
A device ( 11 ) for variable adjustment of the control times of gas change valves ( 9, 10 ) of an internal combustion engine ( 1 ) having a hydraulic phase adjustment apparatus ( 12 ), a camshaft ( 6, 7 ), a volume accumulator ( 18 ), a first fastening element ( 14 ) designed separately to the camshaft ( 6, 7 ) and a central screw ( 13 ), wherein the central screw ( 13 ) extends through the phase adjustment device ( 12 ) and wherein one end of the central screw ( 13 ) contacts an axial side surface of the phase adjustment device ( 12 ) and a first thread ( 15 ) is constructed on the other end.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a device for the variable adjustment of the control times of gas exchange valves of an internal combustion engine with a hydraulic phase adjustment device, a camshaft, a volume accumulator, a fastening element constructed separately from the camshaft, and a central screw, wherein the central screw penetrates the phase adjustment device and wherein an end of the central screw contacts an axial side surface of the phase adjustment device and a first thread is constructed on the other end. 
       BACKGROUND 
       [0002]    In modern internal combustion engines, devices for the variable adjustment of the control times of gas exchange valves are used to be able to vary the phase relation between the crankshaft and camshaft in a defined angle range between a maximum advanced position and a maximum retarded position. The device is integrated in a drive train by means of which torque is transmitted from the crankshaft to the camshaft. This drive train can be realized, for example, as a belt, chain, or gearwheel drive. In addition to the camshaft, the device has a phase adjustment device and a central screw by means of which the phase adjustment device is locked in rotation with the camshaft. The phase adjustment device can be constructed, for example, as an oscillating drive in a vane cell construction with several pressure chambers acting against each other. By adding pressurized medium to a group of pressure chambers while simultaneously discharging pressurized medium from the other group of pressure chambers, the phase relation of the impeller relative to the cell wheel and thus the camshaft relative to the crankshaft can be varied. The pressurized medium flow to and from the pressure chambers is typically regulated by means of a hydraulic proportional directional control valve that can be mounted, for example, within the central screw. 
         [0003]    Such a device is known, for example, from DE 10 2005 060 111 A1. In this embodiment, the central screw is screwed with a solid camshaft, in order to realize the rotationally locked connection between the phase adjustment device and the camshaft. 
         [0004]    From DE 10 2004 026 863 A1, another device is known. In this embodiment, the phase adjustment device is mounted on an installed camshaft that consists of a tube and cams attached to this tube. In this embodiment, the attachment of the phase adjustment device to the camshaft can be realized only with difficulty due to the camshaft constructed as a hollow tube. For this reason, the phase adjustment device is locked in rotation on the camshaft by means of a weld connection. 
         [0005]    Another device is known from DE 102 28 354 A1. In this embodiment, a hollow space that is used as a volume accumulator is provided within the solid camshaft. In operating phases of the internal combustion engine in which sufficient pressurized medium is made available from a pressurized medium pump of the internal combustion engine for operating the phase adjustment device, the volume accumulator fills with pressurized medium. If the demand for pressurized medium of the phase adjustment device increases past the volume flow provided by the pressurized medium pump, the volume accumulator supports the phase adjustment device. 
       SUMMARY 
       [0006]    The present invention is based on the objective of specifying a device with high response behavior and low manufacturing expense. 
         [0007]    This objective is met according to the invention in that the interior of the camshaft has a hollow space in which the fastening element is mounted fixed in position, wherein a second thread is formed on the fastening element and this second thread interacts with the first thread of the central screw such that a rotationally locked connection between the device and the camshaft is produced and wherein, in the hollow space, a volume accumulator with a housing is arranged, wherein an axial end of the housing contacts a contact surface of the fastening element. 
         [0008]    The device has a hydraulic phase adjustment device, a camshaft, a central screw, and a first fastening element. The phase adjustment device is in driven connection with a crankshaft and is locked in rotation with the camshaft by means of the central screw. For this purpose, the central screw penetrates the phase adjustment device, wherein one end of the central screw, for example, a collar, contacts an axial side surface of the phase adjustment device and a first thread, usually an external thread, is formed on the other end. By pressurizing the phase adjustment device with pressurized medium, a phase of the camshaft can be varied relative to the crankshaft. The camshaft has a hollow space in which the fastening element constructed separately from the camshaft is mounted fixed in position, i.e., it cannot be moved in the axial direction or in the peripheral direction under normal loads. The fastening element can be screwed, for example, with the lateral surface of the hollow space. Also conceivable is a non-positive-fit connection. The fastening element has a second thread, usually an internal thread, in which the central screw is screwed, so that the phase adjustment device is locked in rotation with the camshaft. In addition, the device has a volume accumulator that is arranged in the camshaft. The volume accumulator is filled with pressurized medium in phases in which sufficient pressurized medium is available for operating the phase adjustment device. In phases of the insufficient supply of pressurized medium to the phase adjustment device, the pressurized medium stored in the volume accumulator is provided. The volume accumulator has a housing in which the pressurized medium can be stored. In the interior of the housing, for example, a moveable, spring-loaded piston, a flexible membrane, or a bubble filled with gas can be arranged that are used as force accumulators. Here, it is provided that an axial end of the housing contacts a contact surface, usually an axial side surface, of the fastening element. In addition, the housing could be connected to the fastening element. The fastening element is thus used, on one hand, for producing the rotationally locked connection between the phase adjustment device and the camshaft by means of the central screw, wherein, through the use of the fastening element, this connection method can also be used for relatively thin-walled, installed camshafts. In addition, the fastening element is used for the axial position fixing of the housing of the volume accumulator. 
         [0009]    During the installation of the device, initially the fastening element is positioned and fixed in the hollow space of the camshaft. Then the phase adjustment device is locked in rotation with the camshaft by means of the central screw and the volume accumulator is inserted into the camshaft from the end facing away from the phase adjustment device. Then this end of the camshaft is closed with a second fastening element, wherein the second fastening element forces the volume accumulator against the first fastening element, so that the volume accumulator is fixed in the axial direction. 
         [0010]    In one refinement of the invention, it is proposed for the contact surface to have a conical form in the direction of the housing. In this way, the housing of the volume accumulator is centered during the installation of the second fastening element, so that the housing is automatically oriented coaxial to the axis of rotation of the camshaft. For this purpose, advantageously a conical contact surface is likewise provided on the second fastening element. Through the centering of the housing in the hollow space of the camshaft, a ring gap is produced between the housing and the lateral surface of the hollow space, wherein this gap can be used for supplying lubricant to the camshaft bearing points. 
         [0011]    It can also be provided that the first fastening element or the central screw has a pressurized medium channel that runs in the axial direction and opens on the side of the fastening element turned away from the phase adjustment device into the hollow space, for example, the ring gap. Here, the pressurized medium channel can be constructed, for example, as a borehole within the central screw or on an outer lateral surface of the fastening element. It can also be provided that the pressurized medium channel communicates with the volume accumulator or with a camshaft bearing point. 
         [0012]    Thus the fastening element takes on not only the functions of fastening the phase adjustment device to the camshaft and the volume accumulator to the camshaft, but also forms, in a simple, cost-neutral way, parts of the pressurized medium supply system within the device and adjacent assemblies. This reduces the number of components required and the complexity of the device considerably. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Additional features of the invention can be found in the following description and from the drawings in which an embodiment of the invention is shown in simplified form. 
           [0014]    Shown are: 
           [0015]      FIG. 1  only very schematically, an internal combustion engine, 
           [0016]      FIG. 2  a longitudinal section view through a device according to the invention, 
           [0017]      FIG. 3  an enlarged view of the detail X from  FIG. 2 , and 
           [0018]      FIG. 4  a perspective view of a fastening element. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    In  FIG. 1 , an internal combustion engine  1  is sketched, wherein a piston  3  sitting on a crankshaft  2  is indicated in a cylinder  4 . The crankshaft  2  connects to an intake camshaft  6  or exhaust camshaft  7  in the shown embodiment by means of a traction mechanism drive  5 , wherein a first and a second device  11  can provide for a relative rotation between the crankshaft  2  and the camshafts  6 ,  7 . The cams  8  of the camshafts  6 ,  7  actuate one or more intake gas exchange valves  9  and one or more exhaust gas exchange valves  10 , respectively. It can also be provided to equip only one of the camshafts  6 ,  7  with a device or to provide only one camshaft  6 ,  7  that is provided with a device  11 . 
         [0020]      FIG. 2  shows a first embodiment of a device  11  according to the invention in a longitudinal section and cross section, respectively. The device  11  has a phase adjustment device  12 , a camshaft  6 ,  7 , a central screw  13 , and a first fastening element  14 . The phase adjustment device  12  is constructed as a hydraulic adjustment drive, wherein this is set in rotation by the crankshaft  2  by means of a traction mechanism or gearwheel drive  5  and is locked in rotation with the camshaft  6 ,  7 . By supplying pressurized medium to a group of not-shown pressure chambers of the hydraulic adjustment drive of the phase adjustment device  12  while simultaneously discharging pressurized medium from a second group of similarly not shown pressure chambers, the phase position of the camshaft  6 ,  7  can be varied relative to the crankshaft  2  in a defined angle interval. Such phase adjustment devices  12  are known in professional circles and disclosed, for example, in DE 42 18 082 A1 or DE 10 2005 060 111 A1. 
         [0021]    The phase adjustment device  12  is arranged on an axial end of the camshaft  6 ,  7  and contacts an axial stop formed on the camshaft  6 ,  7  in the axial direction. By means of the central screw  13 , the phase adjustment device  12  is locked in rotation with the camshaft  6 ,  7 . For this purpose, the central screw  13  penetrates the phase adjustment device  12 , wherein one end of the central screw  13  is constructed with a collar extending in the radial direction. The collar contacts a side surface of the phase adjustment device  12  turned away from the camshaft  6 ,  7 . A first thread  15  is formed on the other end of the central screw  13 . 
         [0022]    The camshaft  6 ,  7  is constructed as a hollow shaft and has a hollow space  16  that extends along the entire camshaft  6 ,  7 . The first fastening element  14  is arranged within the hollow space  16  and mounted on the camshaft  6 ,  7  fixed in position, i.e., it cannot move in the axial and radial directions. In the shown embodiment, this is realized by means of a press-fit connection between an outer lateral surface of the first fastening element  14  and a lateral surface  16   a  of the hollow space  16 . The first fastening element  14  has, in a central passage borehole, a second thread  17  in which the first thread  15  of the central screw  13  engages, so that the phase adjustment device  12  is locked in rotation with the camshaft  6 ,  7 . 
         [0023]    A volume accumulator  18  is arranged within the hollow space  16  of the camshaft  6 ,  7 . The volume accumulator  18  has a housing  19 , a separating element  20  that is constructed as a piston  20 , and a spring element  21 . The housing  19  has an essentially hollow cylindrical form each with an opening  22  on each axial end side, wherein the housing  19  extends inward in the radial direction on its axial ends  23 . The outer diameter of the housing  19  has a smaller construction than the diameter of the hollow space  16 . The piston  20  is constructed as a thin-walled, pot-shaped sheet-metal component and supported so that it can move in the axial direction within the housing  19 . Here, the piston  20  separates the interior of the housing  19  into a storage space  24  and a complementary space  25 . 
         [0024]    The spring element  21  is arranged in the complementary space  25  and is supported, on one side, on the side of the piston  20  turned away from the storage space  24  and, on the other side, on the area of the housing  19  extending inward in the radial direction. 
         [0025]    The axial ends  23  of the housing  19  each contact a conical contact surface  26  ( FIGS. 2 and 3 ). The first conical contact surface  26  is constructed as an inner cone on the side of the first fastening element  14  turned away from the phase adjustment device  12 . The second contact surface  26  is constructed on a second fastening element  27  that is locked in rotation with the camshaft  6 ,  7  and is arranged on the end of the camshaft  6 ,  7  turned away from the phase adjustment device  12 . Here, the second contact surface  26  is constructed as an outer cone. The volume accumulator  18  is fixed by the contact of the housing  19  on the conical contact surfaces  26  in the hollow space  16  in the axial direction and centered relative to the longitudinal axis of the camshaft  6 ,  7 . Because the outer diameter of the essentially hollow cylindrical housing  19  is less than the inner diameter of the lateral surface  16   a  of the camshaft  6 ,  7 , a ring gap  28  is realized between the housing  19  and the lateral surface  16   a . Thus there is no risk that the housing  19  will be deformed during the positioning in the hollow space  16  due to unevenness on its lateral surface  16   a . This guarantees that the piston  20  does not become jammed within the housing  19 , but instead can move smoothly. This eliminates cost-intensive and time-intensive cutting post processing on the lateral surface  16   a  of the camshaft  6 ,  7 . 
         [0026]    Starting from the first fastening element  14 , the ring gap  28  extends along the entire camshaft  6 ,  7  and covers, in particular, several camshaft bearing points  29 . In the area of the camshaft bearing points  29 , several boreholes  30  are formed on the camshaft  6 ,  7  that communicate, on one side, with the ring gap  28  and, on the other side, with each camshaft bearing point  29 . The ring gap  28  is sealed in the axial direction by the second fastening element  27 . The first fastening element  14  has, on its outer lateral surface, first pressurized medium channels  31  in the form of grooves extending in the axial direction ( FIG. 4 ), so that the ring gap  28  communicates with a mounting area  13   a  of the hollow space  16  in which the central screw  13  is arranged. 
         [0027]    During the operation of the internal combustion engine  1 , pressurized medium fed by a not-shown pressurized medium pump is fed by means of boreholes  30  constructed on the camshaft  6 ,  7  in the area of the first camshaft bearing point  29   a . The pressurized medium is led to the camshaft bearing points  29  via the first pressurized medium channels  31 , the ring gap  28 , and the boreholes  30 . Here, the second fastening element  27  prevents the discharge of pressurized medium on the side of the camshaft  6 ,  7  turned away from the phase adjustment device  12 . 
         [0028]    At the same time, the pressurized medium is led via screw openings  32  into the interior of the hollow central screw  13 . Within the central screw  13 , the pressurized medium is led, on one side, via a not shown, hydraulic proportional directional control valve arranged in the interior of the central screw  13  to the phase adjustment device  12 . Such proportional directional control valves are known, for example, from DE 10 2005 052 481 A1. In addition, when sufficient pressurized medium is being supplied to the phase adjustment device  12 , excess pressurized medium is led via a second pressurized medium channel  33  formed in the central screw  13  to the storage space-side opening  22  of the housing  19  of the volume accumulator  18  and is fed to the storage space  24 . Therefore, the piston  20  is moved against the force of the spring element  21 , wherein the volume of the storage space  24  increases at the expense of the volume of the complementary space  25 . If the pressurized medium volume needed by the phase adjustment device  12  exceeds the pressurized medium volume supplied by the pressurized medium pump, the piston  20  is pushed in the opposite direction due to the force exerted on this piston by the spring element  21  and thus the pressurized medium stored in the volume accumulator  18  is fed via the second pressurized medium channel  33  to the phase adjustment device  12 . 
         [0029]    Thus pressurized medium is supplied to the phase adjustment device  12 , the volume accumulator  18 , and the camshaft bearing points  29  via the interior of the camshaft  6 ,  7 , wherein no additional components are needed. A separate supply of pressurized medium to the camshaft bearing points  29  is not required. 
         [0030]    The second fastening element  27  has an axial, central passage opening  34  by means of which the complementary space  25  communicates with the interior of the internal combustion engine  1 . Thus, air and pressurized medium can escape from the complementary space  25 . 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Internal combustion engine 
           2  Crankshaft 
           3  Piston 
           4  Cylinder 
           5  Traction mechanism drive 
           6  Intake camshaft 
           7  Exhaust camshaft 
           8  Cam 
           9  Intake gas exchange valve 
           10  Exhaust gas exchange valve 
           11  Device 
           12  Phase adjustment device 
           13  Central screw 
           13   a  Mounting area 
           14  First fastening element 
           15  First thread 
           16  Hollow space 
           16   a  Lateral surface 
           17  Second thread 
           18  Volume accumulator 
           19  Housing 
           20  Separating element/piston 
           21  Spring element 
           22  Opening 
           23  Axial end 
           24  Storage space 
           25  Complementary space 
           26  Contact surface 
           27  Second fastening element 
           28  Ring gap 
           29  Camshaft bearing point 
           29   a  First camshaft bearing point 
           30  Borehole 
           31  First pressurized medium channel 
           32  Screw opening 
           33  Second pressurized medium channel 
           34  Passage opening