Abstract:
A valve control device for a gas exchange valve of an internal combustion engine has a cam follower lever interacting with the camshaft. A rocker arm rests on the cam follower lever and actuates the valve. An adjusting device acts on the rocker arm to adjust a valve lift. The rocker arm has first and second control surfaces with first and second radii of curvature, respectively, The cam follower lever has a third control surface with third radius of curvature. The first control surface contacts a fourth control surface of a guide element of the engine with fourth radius of curvature. The second control surface of the rocker arm contacts a valve element. The first to fourth radii of curvature are adjusted such that, when adjusting the valve lift, the valve does not open when the cam follower lever rests on a cam base circle section of the camshaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a valve control device for a gas exchange valve of an internal combustion engine, comprising a cam follower lever interacting with a camshaft and a rocker arm that is contacting the cam follower lever and that actuates the valve. The rocker arm is adjustable for valve lift adjustment by means of an adjusting device. 
         [0002]    Mechanically fully variable valve control devices are known and are employed for reducing fuel consumption in internal combustion engines of passenger cars (DE 101 40 635 A1). The cam follower lever is pivotable about an axis and is positioned with a first roller on a guide and with a second roller on an adjusting device that is in the form of a slidable adjusting bar. For changing the valve lift, the adjusting bar is displaced and the cam follower lever adjusted thereby. The rocker arm is resting on the cam follower lever. The rocker arm is supported with a first lever end on the cylinder head of the internal combustion and actuates with a second lever end the gas exchange valve. As the camshaft rotates, the cam follower lever moves by means of a roller along a curved path of a guide provided at the cylinder head. The manufacture and support of the guide are complex. Extremely high engine speeds are not possible because the main mass of the cam follower lever is high. Mounting of the guide in the cylinder head is also very complex. 
         [0003]    A further valve control device (DE 41 12 833 A1) is known in which the cam follower lever and the rocker arm are formed by two pivotably supported single-arm levers. The cam follower lever is connected with one end rotatably on an eccentric whose eccentric shaft is eccentrically supported in an actuator that is rotatable about a fixed axis associated with the cylinder head. The cam follower lever is resting on the rocker arm which, in turn, is also pivotably supported about a fixed axis that is associated with the cylinder head. By means of the eccentric, the cam follower lever is linearly displaced and in this way the valve lift is adjusted. The adjusting device with the eccentric and the actuator is very complex and expensive. During adjustment, a significant friction force is produced so that the potential for reducing consumption of the internal combustion engine is limited. The eccentric of the adjusting device enables moreover only a minimal adjusting travel so that the valve control device is not suitable for large valve lift adjustments. A lift adjustment of only approximately 50% of the maximum lift can be achieved. 
         [0004]    In another known valve control device (US 2005/0028766 A1), the rocker arm is pivotably supported about an axis. In order to adjust the valve lift, the axis of rotation of the rocker arm or the axis of rotation of the cam follower lever is moved. The movability increases the constructive expenditure of the valve control device. The rocker arm and the cam follower lever are contacting each other with curved control surfaces that are substantially positioned at a slant to the valve axis. This causes significant friction forces when the valve control device is operating. Due to the adjustable elements, the valve control device does not operate at a low noise level. 
         [0005]    In a further known valve control device (US 2006/0021590 A1), the rocker arm is pivotably supported in the cylinder head and is resting on the valve to be actuated. The cam follower lever is designed as a rocker lever that is rotatably supported about a central axis. The axis of rotation of the cam follower lever can be moved along a guide that is secured on the cylinder head in order to adjust the valve clearance. The valve control device has therefore a complex and failure-prone configuration. 
         [0006]    Also, a valve control device is known (DE 29 51 361 A1) in which the rocker arm is pivotably connected at one end to a slide that is slidable transverse to the axis of the valve for valve lift adjustment. For this purpose, a complex adjusting drive is required. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to configure a valve control device for a gas exchange valve of the aforementioned kind such that with a constructively simple configuration a reliable valve lift adjustment even at high engine speeds of the internal combustion engine is ensured wherein the energy consumption for maintaining and adjusting the valve lift is minimal. 
         [0008]    In accordance with the present invention, this is achieved in accordance with the present invention in that the cam follower lever and the rocker arm have curved control surfaces, in that the rocker arm with a first control surface is resting on a curved control surface of a guide element associated with the engine and with a second control surface is resting on a valve element, and in that the radii of curvature of the control surfaces of the cam follower lever, of the guide element, and of the rocker arm are adjusted relative to each other such that, when the valve lift is adjusted, the valve does not open while the cam follower lever is resting on the base circle section of the cam of the camshaft. 
         [0009]    In the valve control device according to the invention, the rocker arm is resting with its curved control surfaces on a guide element associated with the engine and on a valve element. The radii of curvature of the control surfaces of the cam follower lever, of the guide element, and of the rocker arm are adjusted relative to each other such that, when adjusting the magnitude of the valve lift, the valve does not open as long as the cam follower lever is resting on the base circle section of the cam. Due to the radii of curvature that are adjusted relative to each other, it is ensured that, upon adjustment of the valve lift, the gas exchange valve does not open in the compression phase and in the working phase of the internal combustion engine. This adjustment of the valve lift is done when the cam follower lever is resting on the base circle section of the cam of the camshaft. Since the two control surfaces of the rocker arm and the control surface of the guide element are curved, only a very minimal friction occurs upon operation of the valve control device so that the valve lift adjustment can be carried out reliably. 
         [0010]    In a preferred embodiment, the control surface of the guide element has a greater radius of curvature than the first control surface of the rocker arm. Accordingly, between the two control surfaces of the guide element and of the rocker arm, only a linear contact is substantially existing, which contributes to a low-friction operation and adjustment of the rocker arm relative to the guide element. 
         [0011]    However, it is also possible that both control surfaces of guide element and rocker arm have the same radius of curvature. 
         [0012]    The second control surface of the rocker arm, with which it is resting on the guide element, has advantageously a smaller radius of curvature than the first control surface of the rocker arm and/or the control surface of the guide element. 
         [0013]    A contribution to a low-friction operation of the valve control device is provided in an advantageous manner when the cam follower lever is resting with a curved control surface on the rocker arm. 
         [0014]    Advantageously, the control surface of the cam follower lever has a first control surface section with a section radius of curvature. The cam follower lever is pivoted by the camshaft in a known way back and forth wherein the rocker arm resting on the cam follower lever is moved by the required magnitude in order to open or close the valve. 
         [0015]    Advantageously, the first control surface section of the cam follower lever passes, continuously curved, into a second control surface section which is curved opposite to the first control surface section. Due to the differently oriented curvature of the two control surface sections, the rocker arm can be adjusted such that for one revolution of the camshaft the valve will not open depending on whether the contact between the cam follower lever and the rocker arm occurs at the first or the second control surface section. By means of the two control surface sections it is possible to adjust in a continuous way (no steps) the valve lift from 0 to a maximum. 
         [0016]    In order to achieve a friction that is as minimal as possible, the rocker arm is advantageously resting with a freely rotating roller on the control surface of the cam follower lever. 
         [0017]    In an especially advantageous embodiment, the rocker arm is provided with a through bore through which the adjusting device extends. In this way, there is the possibility to mount the adjusting device while the rocker arm is already installed. On the other hand, in this way there is also the possibility to mount the rocker arm after the adjusting device has already been mounted. In both cases, the rocker arm can be demounted, if needed, without the adjusting device having to be removed also. 
         [0018]    A very compact configuration of the valve control device results when the adjusting device has a control shaft which is provided with a control surface on which the rocker arm is resting. The control shaft requires only little space for installation. In particular, the control shaft can be used for several valve control devices provided within the internal combustion engine. The through opening is designed advantageously such that it is open toward the edge of the rocker arm. This facilitates mounting of the control shaft and/or of the rocker arm. 
         [0019]    Preferably, the control surface is the circumferential surface of an eccentric member of the control shaft. Since an internal combustion engine has several valve control devices for the gas exchange valves, it is thus possible to provide a common control shaft for all valve control devices. The eccentric member of the control shaft is designed such that it does not project past the circumference of the control shaft. Accordingly, the outer diameter of the control shaft determines the size of the through opening of the rocker arm. 
         [0020]    The rocker arm is positioned advantageously with a freely rotating roller on the control surface of the control shaft so that in this contact area only minimal frictional forces occur. 
         [0021]    In another embodiment according to the invention, the rocker arm is floatingly supported. No complex rotary support is required so that the constructive configuration of the valve control device and thus of its manufacturing costs are minimal. The rocker arm is secured between the adjusting device and the cam follower lever. When a valve lift adjustment is to be performed, the floatingly supported rocker arm is displaced transversely to the axis of the valve so that the relative position of the cam follower lever and of the rocker arm relative to each other is changed. 
         [0022]    The guide element is advantageously adjustable transversely to the axis of the control shaft. In this way, the position of the rocker arm can be adjusted precisely. 
         [0023]    The rocker arm is secured in the mounted position in that the control shaft and the cam follower lever are resting on opposite sides of the rocker arm. In combination with the contact of the rocker arm on the guide element and on the valve element, it is thus ensured in a simple way that the rocker arm maintains its respectively adjusted position reliably. In any position of the control shaft and of the cam follower lever, the rocker arm is positioned transverse to the valve axis between these two elements of the valve control device. 
         [0024]    In an advantageous embodiment the adjustment of the rocker arm is realized by means of the valve element and/or by means of an eccentrically adjustable bearing axis of a roller of the cam follower lever that is resting on the camshaft and/or by means of an eccentrically adjustable bearing axis of the roller of the rocker arm resting on the camshaft follower lever and/or by means of an eccentrically adjustable bearing axis of the roller of the rocker arm that is resting on the control shaft and/or by means of the adjustable guide element. The described adjusting possibilities can be provided each individually but also in any combination with each other on the valve control device. Depending on the situation of use of the valve control device, there is therefore the possibility to provide the various adjustments such that the valve lift adjustment is possible in an optimal way. 
         [0025]    In an advantageous embodiment, a valve control arrangement is provided that comprises two of the valve control devices as described above that have different control surfaces on the cam follower levers and/or different control surfaces on the control shafts. In this way, the valve lifts of the different valve control devices can be designed differently. 
         [0026]    The present invention not only results from the individual claims but also from the features and disclosures provided in the drawings and the description. Accordingly, features and disclosures that are not claimed are considered to be important for the invention inasmuch as they are individually or in combination novel relative to the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0027]      FIG. 1  is a schematic illustration of a valve control device according to the invention with a rocker arm in a first position. 
           [0028]      FIG. 2  shows the valve control device according to  FIG. 1  with the rocker arm in a second position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    By means of the valve control device, the lift of the gas exchange valves can be adjusted continuously and individually up to the range of very high engine speeds of the internal combustion engine. The energy consumption for maintaining and adjusting the adjustable valve lift is kept minimal. The valve control device is characterized by an inexpensive manufacture and can be mounted easily. 
         [0030]      FIG. 1  shows a valve  1  to be controlled that has a valve stem  2  which has at one end a valve plate  3  with which a valve opening  4  can be opened and closed. In the position according to  FIG. 1 , the valve plate  3  closes the valve opening  4  of the internal combustion engine. At the other end, the valve stem  2  is provided with a valve cap  5 . At the cap&#39;s underside, a pressure spring  6  is supported which loads the valve stem  2  in the direction of the closed position of the valve plate  3 . The pressure spring  6  is supported also on a cylinder head  7  of the internal combustion engine. 
         [0031]    At the other side of the valve cap  5 , a rocker arm  8  is resting which is interacting with a cam follower lever  9  that is pivoted by a camshaft  10  whose cams  11  each interact with a respective cam follower lever  9 . 
         [0032]    The camshaft  10  rotates about axis  12 . The cam follower lever  9  is resting with a roller  13  on the cam  11 ; the roller  13  is supported rotatably about axis  14  on the cam follower lever  9 . The cam follower lever  9  is supported about stationary axis  15  pivotably on the cylinder head  7 . 
         [0033]    The cam follower lever  9  has a radial arm  16  projecting radially relative to pivot axis  15 ; the roller  13  is rotatably supported on the radial arm  16 . The width of the radial arm  16  is smaller than the outer diameter of the roller  13  so that the cam follower lever  9  is resting only with the roller  13  on the cam  11 . 
         [0034]    The rocker arm  8  is supported on a guide element  17  that is seated on support element  18 . It is advantageously supported to be adjustable in axial direction on the cylinder head  7 . The support element  18  can be designed, for example, like a screw so that a continuous adjustment of the guide element  17  is possible. The support element  18  can also be hydraulically adjustable. 
         [0035]    The guide element  17  has on its side that is facing the rocker arm  8  a concave control surface  19  that has a radius of curvature R 2 . On the curved control surface  19  of the guide element  17  the rocker arm  8  is resting with a control surface  20 . Control surface  20  is convexly curved and has a radius of curvature R 4  that is smaller than the radius of curvature R 2  of the curved control surface  19 . The control surface  20  is advantageously provided on a projecting curved arm  21  of the rocker arm  8 . The curved arm  21  is provided on its side opposite the control surface  20  with a concavely curved surface  22  that delimits a through opening  36  for a control shaft  23  partially. The control shaft  23  is designed as an eccentric shaft. By rotation of the eccentric shaft  23  about axis  24 , the rocker arm  8  is adjusted transversely to axis  24  and to the valve axis. The maximum adjustment travel is determined by the eccentricity of the control shaft  23 . By means of the control shaft  23 , the magnitude of the valve lift is adjusted. 
         [0036]    The contact of the rocker arm  8  on the control shaft  23  is realized by means of roller  25  which is supported on the rocker arm  8  so as to be freely rotatable about axis  26 . The roller  25  projects past the surface  22  and is resting on a circumferential surface  27   a  of an eccentric member  27  of the control shaft  23 . 
         [0037]    The contact area  28  between the two control surfaces  19 ,  20  and the contact area  29  between the roller  25  and the eccentric member  27  are located on opposite sides of the axis  24  of the control shaft  23  as well as at different levels. 
         [0038]    The rocker arm  8  is positioned on the valve cap  5  with a control surface  30  that is convexly curved and has the radius of curvature R 3 . The radius of curvature R 3  is smaller than the radii of curvature R 2  and R 4 . The contact side of the valve cap  5  is planar. As a result of the curved control surface  30  the friction between the rocker arm  8  and the valve cap  5  is minimal. The control surface  30  is advantageously provided on a projecting arm  31  of the rocker arm  8 . 
         [0039]    The contact of the rocker arm  8  on the cam follower lever  9  is realized by a freely rotating roller  32  that is rotatable about axis  33  and is projecting past the rocker arm  8  in the direction of the cam follower lever  9 . The roller  32  is resting on a curved control surface  34  of the cam follower lever  9 . The curved control surface  34  has a control surface section  34   a  which extends in a convex shape with a radius of curvature R 1  about axis of rotation  15  of the cam follower lever  9 . The control surface section  34   a  passes continuously curved into a concave control surface section  34   b.  As a result of this continuous transition, the roller  32  of the rocker arm  8  upon actuation of the valve  1  can pass without problem from one of the control surface sections onto the other one of the control surface sections. 
         [0040]    The rocker arm  8  is provided for passage of the control shaft  23  with an opening  36  which is delimited in the direction of the guide element  17  by the curved arm  21 . In this way, it is possible to mount the control shaft  23  after the rocker arm  8  has already been mounted. On the other hand, it is possible in this way to mount or demount the rocker arm  8  even though the control shaft  23  is already installed. 
         [0041]    The surface  22  forms also the lateral surface of a projecting arm  37  on which the roller  25  is supported. The through opening  36  is open toward the edge of the rocker arm  8  so that mounting of the control shaft  23  and/or of the rocker arm  8  is possible in a simple way. 
         [0042]    In the area of the roller  32 , the rocker arm  8  has a projecting arm  38 ; the roller  32  projects past this arm  38  with a portion of its circumference. 
         [0043]    The radii of curvature R 1  to R 4  of the curved control surfaces on the rocker arm  8  and on the cam follower lever  9  are adjusted relative to each other such that, upon adjustment of the valve lift through the control shaft  23 , the gas exchange valve  1  is not opened as long as the roller  13  of the camshaft follower lever  9  is in contact with the base circle section  39  of the cam  11 . In  FIG. 1  the roller  13  is resting on this base circle section  39  of the cam  11 . As a result of the adjustment of the radii of curvature R 1  to R 4 , it is ensured that, when adjusting the valve lift, the valve  1  is not opened in the compression phase and in the working phase of the internal combustion. The adjustment of the magnitude of the valve lift is always realized once the roller  13  is resting on the base circle section  39  of the cam  11 . When subsequently the camshaft  10  rotates about its axis  12 , the cam follower lever  9  is pivoted about its axis  15  so that the rocker arm  8  is pivoted accordingly. As this happens, the roller  32  moves along the control surface  34  of the cam follower lever  9 . The valve  1  is opened and closed in accordance with the adjusted lift. The curved control surface  30  of the rocker arm  8  enables a reliable lift of the valve  1 . 
         [0044]    In  FIG. 2 , the maximum adjustment of the rocker arm  8  by the control shaft  23  is illustrated. In comparison to the position according to  FIG. 1 , the control shaft  23  is rotated by 180°. Since the rocker arm  8  is resting by means of roller  25  on the eccentric member  27  of the control shaft  23 , the rocker arm  8  is moved in  FIG. 2  to the right. The arm  21  glides with its control surface  20  on the curved control surface  19  of the guide element  17 . At the same time, the rocker arm  8  glides with the control surface  30  on the valve cap  5 . 
         [0045]    Since the rocker arm  8  is resting with its roller  32  on the control surface  34  of the cam follower lever  9 , the movement of the rocker arm  8  by means of the control shaft  23  has also the result that the roller  32  is moved along the control surface  34  of the cam follower lever  9  by an appropriate travel. As a result of the curvature of the control surface  34 , the rocker arm  8  is not only moved transverse to the axis of the valve stem  2  but is also minimally pivoted. 
         [0046]    Since the rollers  25 ,  32  of the rocker arm  8  are supported to be freely rotatable, the adjustment of the rocker arm  8  can be carried out reliably with minimal friction. The curved control surfaces  20 ,  30  assist in the low-friction adjustment of the rocker arm  8 . 
         [0047]    The floatingly supported rocker arm  8  is reliably secured by the control shaft  23  (i.e., by the contact of the roller  25  on the eccentric member  27 ), by the roller  32 , by the guide element  17 , and by the valve cap  5 . The cam follower lever  9  which is supported by roller  13  on the camshaft  10  forms the support for the roller  32  of the rocker arm  8 . The rocker arm  8  is loaded by means of the cam follower lever  9  toward the control shaft  23  and the valve cap  5 . In this way, the rocker arm  8  is securely held in its mounted position. The control shaft  23  and the cam follower lever  9  are resting in any position on opposite sides of the rocker arm  8  so that the rocker arm  8  is positionally secured in its longitudinal direction transverse to the axis of the valve  1 . 
         [0048]    The rocker arm  8  is a part that can be manufactured in a simple way; on the rocker arm  8 , the freely rotatable rollers  25 ,  32  that have a spacing relative to each other can be mounted in a simple way. The adjustment of the position of the rocker arm  8  is possible in a simple way. For example, the guide element  17  can be fine-adjusted by means of the support element  18  in the axial direction of the support element  18 . The adjusting direction is advantageously parallel to the valve axis. A further possibility resides in that the roller  13  of the cam follower lever  9  is designed to be eccentrically adjustable. The adjusting direction is advantageously parallel to the valve axis. A further possibility of positional adjustment resides in that the roller  32  with which the rocker arm  8  is resting on the cam follower lever  9  is designed to be adjustable eccentrically. 
         [0049]    The described adjusting possibilities can be provided individually or in any combination with each other. In this way, there is the possibility to fine-adjust the rocker arm  8  optimally in its mounted position. 
         [0050]    In the internal combustion engine, the valve control devices can be designed such that two neighboring valve control devices for valve lift adjustment in the cylinder head  7  have different control surfaces  34  on the cam follower lever  9  and/or different control surfaces  27   a  on the eccentric member  27  of the control shaft  23 . 
         [0051]    In the illustrated and preferred embodiment, the curved control surface  19  of the guide element  17  and the control surface  20  of the rocker arm  8  have different radii of curvature. In this way it is achieved that the rocker arm  8  and the guide element  17  substantially are resting on each other with linear contact. 
         [0052]    Basically, it is however also possible that the control surfaces  19  and  20  have the same radius of curvature. The described adjustment of the rocker arm  8  is then possible also. 
         [0053]    When the camshaft  10  upon operation of the internal combustion engine rotates about its axis  12 , the valve stem  2  is opened and closed by the cam follower lever  9  and the rocker arm  8  wherein the lift travel depends on the adjusted position of the rocker arm  8 . The pressure spring  6  ensures that the valve cap  5  is always contacting the rocker arm  8  and the valve plate  3  is returned into its closed position. Advantageously, the valve cap  5  is axially slidable relative to the valve stem  2  to a limited extent. In this way, possible clearance between the valve cap  5  and the control surface  30  of the rocker arm  8  can be compensated. In this case, the valve cap  5  is seated on a bolt  41  that projects into the valve stem  2  and which is loaded by the force of a pressure spring  42  surrounding the bolt  41 . The spring  42  is supported on the end face of the valve stem  2  as well as on the thicker area  43  of the bolt  41 . The pressure spring  42  ensures that, when the valve  1  is closed, the valve cap  5  is resting on the control surface  30  of the rocker arm  8 . 
         [0054]    The specification incorporates by reference the entire disclosure of German priority document 10 2013 013 913.9 having a filing date of Aug. 16, 2013. 
         [0055]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.