Abstract:
A valve stroke control for an internal combustion engine of a motor vehicle has a control device for adjusting a valve stroke. It interacts with a camshaft and a control shaft. The control device is actuated by a hydraulic medium and has a first control element and a second control element movable relative to one another. The first control element is sleeve-shaped and the second control element is received in the first control element. A rocker lever is acted on by the camshaft. The first control element is supported on the rocker lever and the second control element is supported on the control shaft.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention.  
           [0002]    The invention relates to a valve stroke control for internal combustion engines of motor vehicles, comprising at least one control device provided for adjusting the stroke of valves, wherein the at least one control device interacts with at least one camshaft and at least one control shaft.  
           [0003]    2. Description of the Related Art.  
           [0004]    By means of valve stroke controls, the valves of an internal combustion engine of motor vehicles are opened only to such an extent that the required fuel quantity for the respective output demand of the engine is injected into the combustion chamber. The control shaft acts on a control element in the form of a lever which acts on the valve shaft. This mechanical control element is prone to failure and does not enable a precise adjustment of the valve stroke.  
         SUMMARY OF INVENTION  
         [0005]    It is an object of the present invention to configured the valve stroke control of the aforementioned kind such that the valve stroke can be adjusted precisely and reliably in a constructively simple way.  
           [0006]    In accordance with the present invention, this is achieved in that the control device is actuated by a hydraulic medium.  
           [0007]    The control device is thus hydraulically actuated in accordance with the present invention, and, since the hydraulic medium is present within a motor vehicle anyway, the control device can be supplied easily with the required hydraulic medium. By means of the control device the stroke of the valve can be adjusted simply and precisely. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 illustrates a first adjusting position of a first embodiment of a valve stroke control of the present invention in connection with an overhead camshaft.  
         [0009]    [0009]FIG. 2 shows a second position of the valve stroke control according to the present invention.  
         [0010]    [0010]FIG. 3 shows a third position of the valve stroke control according to the present invention.  
         [0011]    [0011]FIG. 4 shows a fourth position of the valve stroke control according to the present invention.  
         [0012]    [0012]FIG. 5 shows a fifth position of the valve stroke control according to the present invention.  
         [0013]    [0013]FIG. 6 is a sixth position of the valve stroke control according to the present invention.  
         [0014]    [0014]FIG. 7 shows a second embodiment of a valve stroke control according to the invention with the camshaft mounted in the cylinder block. 
     
    
     DETAILED DESCRIPTION  
       [0015]    The valve stroke control described in the following is designed to control or change the stroke of valves in internal combustion engines preferably in a variable way. FIG. 1 shows a cylinder head  1  of an internal combustion engine in which, depending on the engine type, a different number of combustion chambers and corresponding valves  2  are provided. In FIG. 1, one of these valves  2  is illustrated. It is provided with a valve disk  3  with which an intake opening  4  into the combustion chamber can be closed. The valve disk  3  is mounted on the end of a valve shaft  5  which can be moved counter to the force of at least one pressure spring  6  into an open position. At the end of the valve shaft  5  opposite the valve disk  3 , a spring plate  7  is provided. The end of the pressure spring  6  is supported on the valve plate  7 . The other end of the spring  6  is supported on the cylinder head. In this way, the valve disk  3  is pulled by the pressure spring  6  into the closed position illustrated in FIG. 1.  
         [0016]    The end  8  of the valve shaft  5  projecting past the spring plate  7  is spherical and positioned in a cup-shaped receptacle  9  provided at the free end of an arm  10  of a two-arm rocker lever  11 . The rocker lever  11  is secured transversely to an imaginary pivot axis in a fork member  12  provided on the cylinder head  1 . The other arm  13  of the rocker lever  11  rests against an adjusting cylinder  14  which is slidably mounted in a bore  15  in the cylinder head  1 . The adjusting cylinder  14  receives a hollow piston  16  resting against a cam  17  of a control shaft  18 . The hollow piston  16  receives at least one pressure spring  19  which is supported with one end on the bottom  20  of the hollow piston  16  and with the other end on a bottom  21  of the adjusting cylinder  14 . The hollow piston  16  is loaded by the pressure spring  19  always such that its bottom  20  rests at all times against a control curve  22  of the cam  17  of the control shaft  18 . The hollow piston  16  is slidably and sealingly guided within the adjusting cylinder  14 . Since the hollow piston  16  receives the pressure spring  19 , a very compact configuration results.  
         [0017]    When sufficient mounting space is available, the part  16  can also be of a solid construction. In this case, a greater size of the control device results because the pressure spring  19  is positioned between the end face of the part  16  and the bottom  21  of the adjusting cylinder  14 .  
         [0018]    The adjusting cylinder  14  is surrounded about a portion of its length by an annular chamber  23  provided within the cylinder head  1 . A bore  24  opens into the annular chamber  23 . The annular chamber  23  is formed by a section of the bore  15  which has a widened diameter.  
         [0019]    The adjusting cylinder  14  has penetrations  26  that are arranged in the cylinder wall  25  at a minimal spacing from its bottom  21  and are distributed about the circumference. The penetrations  26  are preferably in the form of bores providing connections by means of which the annular chamber  23  is connected with the interior  27  of the adjusting cylinder  14 .  
         [0020]    The two ends of the lever arms  10 ,  13  are angled in a direction toward the valve shaft  5  and the adjusting cylinder  14 , respectively. On the opposed side, the rocker lever  11  is provided with a projection or raised portion  28  which extends across most of the length of the rocker lever  11  and against which a camshaft  29  rests. By means of the projection  28  the rocker lever  11  is pivoted for opening the valve  2  in a way to be described in the following.  
         [0021]    The rocker lever  11  is not fixedly supported but rests with the ends of its arms  10 ,  13  against the valve shaft  5  and against the adjusting cylinder  14 .  
         [0022]    [0022]FIG. 1 shows the initial position of the valve control in which the cam  30  of the camshaft  29  is not engaged by the rocker lever  11 . The control shaft  18  is rotated into a position in which a contact area  31  between the control curve  22  and the bottom  20  of the hollow piston  16  has the greatest spacing relative to the axis  32  of the control shaft  18 . In this position, the valve  2  is closed. The hollow piston  16  has a spacing from the bottom  21  of the adjusting cylinder  14  whose penetrations (bores)  26  connect the annular chamber  23  with the interior  27  of the adjusting cylinder  14  as well as with the interior  33  of the hollow piston  16 .  
         [0023]    When the camshaft  29  is rotated in the direction of arrow  34  (FIG. 2), the cam  30  reaches the area of the arm  13  the rocker lever  11 . The lever  11  is thus moved in the clockwise direction thereby moving the adjusting cylinder  14  against the force of the pressure spring  19 . Since the control shaft  18  is not rotated, the hollow piston  16  is supported on the control curve  22  of the cam  17  of the control shaft  18 . The adjusting cylinder  14  is moved to such an extent on the hollow piston  16  that the penetrations (bores)  26  in the cylinder wall  25  of the adjusting cylinder  14  are closed by the hollow piston  16 . In this way, the connection between the interiors  27 ,  33  of the adjusting cylinder  14  and of the hollow piston  16  is closed relative to the annular chamber  23 . The hydraulic medium which is contained in both interiors  27 ,  33  is in this way enclosed so that the adjusting cylinder  14  cannot be moved relative to the hollow piston  16 . As long as the penetrations/bores  26  of the adjusting cylinder  14  are not yet closed, the hydraulic medium is displaced out of the interiors  27 ,  33  via the penetrations (bores)  26  and the annular chamber  23  back into the bore  24  when the adjusting cylinder  14  is moved, and in this way the hydraulic medium is returned into the hydraulic medium circulation.  
         [0024]    As soon as the bores  26  are closed by the hollow piston  16 , the adjusting cylinder  14  and the hollow piston  16  act as a fixed bearing for the rocker lever  11 .  
         [0025]    As shown in FIG. 2, the cam  30  at this point is in the area of the arms  13  of the rocker lever  11 . The valve  2  at this point is still in the closed position because the rocker lever  11 , when the described rocking movement occurs, is pivoted only about the spherical end  8  of the valve shaft  5 .  
         [0026]    When the camshaft  29  is rotated from the position according to FIG. 2 farther into the rotary direction  34  (FIG. 3), the rocker lever  11  is pivoted counter to the clockwise direction because the arm  13  of the rocker lever  11  is supported on the adjusting cylinder  14  acting as a fixed bearing. The valve shaft  5  is moved counter to the force of the pressure spring  6  so that the valve disk  3  is lifted off the valve seat and opens the intake opening  4  into the combustion chamber.  
         [0027]    [0027]FIG. 4 shows the maximum valve stroke. It is reached when the camshaft  29  has been rotated to such an extent that the cam  30  projects farthest in the direction towards the rocker lever  11 . In this position (FIG. 4) the rocker lever  11  has been pivoted farthest counter to the clockwise direction so that the valve shaft  5  is moved farthest. The valve  2  has thus performed the greatest stroke. The valve disk  3  is moved farthest away from the valve seat.  
         [0028]    When the camshaft  29  is rotated farther in the direction  34 , the rocker lever  11  is pivoted back in the clockwise direction by the valve shaft  5 . By means of the spring plate  7 , the valve shaft  5  is returned by the pressure spring  6  so that the rocker lever  11  is pivoted by the corresponding amount. The camshaft  29  and the rocker lever  11  finally reach again the position according to FIG. 1 in which the valve  2  closes the intake opening  4  into the combustion chamber. As soon as the valve  2  is closed, the adjusting cylinder  14  is relieved so that the adjusting cylinder  14  is returned by the force of the pressure spring  19  relative to the hollow piston  16 . As soon as the hollow piston  16  releases the penetrations or bores  26  in the cylinder wall  25  of the adjusting cylinder  14 , the hydraulic medium can flow back via the bore  24  and the annular chamber  23  into the interiors  27 ,  33  of the adjusting cylinder  14  and of the hollow piston  16 . Because the spring chamber between the adjusting cylinder  14  and the hollow piston  16  is enlarged when this occurs, the hydraulic medium is sucked in from the bore  24 .  
         [0029]    As a result of the described configuration, a valve play compensation is also achieved at the same time so that the valve can be opened and closed reliably.  
         [0030]    The force of the pressure spring  19  in the adjusting cylinder  14  is significantly smaller thah the force of the pressure spring  6  with which the valve  2  is biased. In any case, the force of the pressure spring  19  is however so large that a safe contact of the adjusting cylinder  14  and of the hollow piston  16  on the rocker lever  11  and on the control curve  22  of the control shaft  18  is ensured.  
         [0031]    The relative play between the hollow piston  16  and the adjusting cylinder  14  is so minimal that a sealing function is provided. The hydraulic medium therefore does not reach the exterior so that leakage losses are prevented or are so small that they can be neglected.  
         [0032]    Each cylinder of the combustion engine is provided with one lever  11  and the corresponding valve stroke control. On the control shaft  18 , depending on the control strategy, several or only one control curve  22  can be provided.  
         [0033]    By means of the control shaft  18 , the valve stroke can be changed. The valve stroke can be adjusted such that only so much fuel is injected into the corresponding combustion chamber as is required for the momentary output of the combustion engine.  
         [0034]    By rotating the control shaft  18 , the spacing of the hollow piston  16  from the axis  32  of the control shaft  18  can be changed as a function of the rotary position of the control shaft. In FIGS. 1 through 4, the control shaft  18  has been rotated such that the hollow piston  16  has the greatest spacing from the axis  32  of the control shaft  18 . FIGS. 5 and 6 show the situation that the hollow piston  16  has the smallest spacing from the axis  32  of the control shaft  18 . In this position, the control shaft  18  has been rotated away from the position according to FIGS. 1 through 4 in the clockwise direction until the control shaft  5  has reached the position according to FIGS. 5 and 6. The hollow piston  16  rests with its bottom  20  under the force of the pressure spring  19  against the control curve  22  of the cam  17  of the control shaft  18 . The hollow piston  16  has been moved so far out of the adjusting cylinder  14  that the end face  35  of the hollow piston  16  is positioned in the area underneath the penetrations or bores  26  in the cylinder wall  25  of the adjusting cylinder  14 . The interiors  27 ,  33  of the adjusting cylinder  14  and of the hollow piston  16  are thus connected with the annular chamber  23  and the bore  24 .  
         [0035]    When the camshaft  29  is rotated in the direction  34 , the rocker lever  11  is tilted in the clockwise direction, as described in connection with FIGS. 1 through 4, such that the adjusting cylinder  14  is moved relative to the hollow piston  16  against the force of the pressure spring  19 . The hollow piston  16  is supported on the control curve  22  of the control shaft  18 . Since the control shaft  18  has been rotated such that the spacing between the hollow piston  16  and the axis  32  of the control shall  18  is minimal, the adjusting cylinder  14 , in comparison to the position of the control shaft according to FIGS. 1 through 4, is moved significantly farther until the penetrations or bores  26  of the adjusting cylinder  14  are closed by the hollow piston  16 . Now the adjusting cylinder  14  and the hollow piston  16  act in the described way as fixed bearings for the rocker lever  11 . As a result of the great movement travel of the adjusting cylinder  14  the rocker lever  111  is pivoted to a great extent in the clockwise direction. This has the result that by rotation of the camshaft  29  the valve  2  is not opened at all. As shown in FIG. 6, the cam  30  of the camshaft  29  is in its maximum stroke position without the rocker lever  11  having been pivoted such that the valve  2  is opened. By means of the control shaft  18  it is thus possible to provide a zero stroke for the valve  2 .  
         [0036]    Depending on the rotary position of the control shaft  18 , the stroke of the valve  2  can be adjusted between the maximum stroke (FIGS. 1 through 4) and the zero stroke (FIG. 5 and FIG. 6). When the control shaft  18  is in intermediate positions between the maximum position (FIGS. 1 through 4) and the minimum position (FIGS. 5 and 6), the stroke of the valve  2  can be adjusted continuously between the maximum stroke according to FIGS. 1 through 4 and the zero stroke according to FIGS. 5 and 6. In this way, the amount of fuel to be injected into the combustion chamber for the current output demand of the internal combustion engine can be precisely adjusted in a very simple way.  
         [0037]    [0037]FIG. 7 shows that the position of the camshaft  29  and control shaft  18  can be exchanged. The function of the valve control does not changed when doing so. The hollow piston  16  is positioned on the projection  28  of the rocker lever  11  under the force of the pressure spring  19 . The rocker lever  11  rests with the angled end of its arm  13  against the camshaft  29 .  
         [0038]    The adjusting cylinder  14  rests against the control curve  22  of the cam  17  of the control shaft  18 . It is rotated such that the adjusting cylinder  14  has the smallest spacing from the axis  32  of the control shaft  18 . The end face  35  of the hollow piston  16  is positioned at a spacing from the penetrations or bores  26  in the cylinder wall  25  of the adjusting cylinder  14 . The penetrations or bores  26  which are provided corresponding to the preceding embodiments closely adjacent to the bottom of the adjusting cylinder  14  are thus not closed by the hollow piston  16 . The hydraulic medium can flow from the bore  24  into the annular chamber  23  and from there, by means of the penetrations or bores  26 , into the interiors  27  and  33  of the adjusting cylinder  14  and of the hollow piston  16 .  
         [0039]    When the camshaft  29  rotates, the rocker lever  11  is tilted by the cam  30  first in a counter-clockwise direction wherein the rocker lever  11  is supported with its arm  10  on the end face of the valve shaft  5 . Since the force of the pressure spring  6  is greater than the force of the pressure spring  19 , the valve shaft  5  is not yet moved upon tilting of the rocker lever  11  by the cam  30  so that the valve  2  cannot be opened during the tilting action. The hollow piston  16  is moved against the force of the pressure spring  19  while the adjusting cylinder  14  is supported on the control curve  22  of the control shaft  18 . Upon movement of the hollow piston  16 , the interior  27 ,  33  becomes smaller. The hydraulic medium contained therein is then displaced via the penetrations or bores  26  of the adjusting cylinder  14  and the annular chamber  23  into the bore  24  and back into the hydraulic chamber of the engine. As soon as the hollow piston  16  closes the penetrations or bores  26 , the adjusting cylinder  14  and the hollow piston  16  provide a fixed bearing for the rocker lever  11 .  
         [0040]    This position of the hollow piston  16  is reached according to the preceding embodiments already when the cam  30  of the camshaft  29  has not yet reached its maximum adjusting position in which the cam  30 , relative to the position according to FIG. 7, is located on the diametrically opposed side of the camshaft  29 . In this way, the rocker lever  11  upon further rotation of the camshaft  29  is tilted in the counter-clockwise direction so that the valve shaft  5  is moved counter to the force of the pressure spring  6  and the valve  2  is opened in this way.  
         [0041]    Upon further rotation of the camshaft  29 , the valve  2  closes again in that the valve shaft  5  is pushed back by the spring plate  7  by means of the pressure spring  6  acting on it. The rocker lever  11  is tilted in the clockwise direction. As soon as the valve  2  is closed, the cam  30  of the camshaft  29  reaches again such a position that the pressure spring  19  returns the hollow piston  16  and in this way returns the rocker lever  11  into the initial position according to FIG. 7. As soon as the hollow piston  16  releases the penetrations or bores  26  in the adjusting cylinder  14 , the hydraulic medium is again sucked in from the bore  24 .  
         [0042]    In order to change the stroke of the valve  2 , the control shaft  18  is rotated.  
         [0043]    Depending on the rotary position of the control shaft  18  or its cam  17 , the stroke of the valve  2  is changed in a variable way. This achieves that the fuel is injected only in such an amount into the combustion chamber of the internal combustion engine as is required for the momentary output of the internal combustion engine.  
         [0044]    The hydraulic medium which is required for the operation of the control device  14 ,  16  can also be provided in a preloaded storage device. When the hollow piston  16  releases the bores  26  in the adjusting cylinder  14 , the hydraulic medium is sucked in from the preloaded storage device. On the other hand, the hydraulic medium can be displaced upon reducing the interiors  27 ,  33  of the control device  14 ,  16  back into the storage device.  
         [0045]    The circulation of the hydraulic medium in connection with the pre-loaded storage device can be a closed system. However, it is also possible to connect the preloaded storage device by means of a check valve to the motor oil circulation and to supply it to the valve stroke control by means of the motor oil circulation. This provides, in particular, a leakage compensation.  
         [0046]    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.