Patent Publication Number: US-6907852-B2

Title: Valve operating device for variable stroke adjustment of a charge exchange valve of an internal combustion engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of international patent application no. PCT/EP02/04332, filed Apr. 19, 2002, designating the United States of America, and published in German as WO 02/092972, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany Patent Application No. DE 101 23 186.5, filed May 12, 2001. 

   BACKGROUND AND SUMMARY OF THE INVENTION 
   The invention relates to a valve operating device for the variable adjustment of the stroke of a charge exchange valve of an internal combustion engine, wherein the charge exchange valve is in active connection with a wheel rotatable about an axis of rotation, with the interposition of a transfer element, having a control path, comprising an idle stroke track and a working stroke track, in an end portion of a lever operated by a cam of a camshaft for lifting the charge exchange valve, wherein the lever associated under spring thrust with the cam on a curved path is supported at the other end along an arcuate path for variable stroke adjustment through a pivot point that is variable in position and fixable. 
   A valve operating device of this kind is disclosed in DE 197 08484 A1, wherein the lever has, in its end area remote from the control path, an arcuately shaped set of teeth for engagement in teeth of a control shaft which serves as an adjustment device for varying the fulcrum position associated with a particular stroke of the charge exchange valve. The pivot point of the lever is located in this case at the point of contact with the reference circles. 
   With this arrangement, when the cam of an adjacent camshaft acts upon the lever, it is brought about that the latter rolls in the teeth of the stationary control shaft and at the same time, in addition to a turning movement or rotatory movement with respect to the wheel of the transmission element, a translational component of movement also occurs with the circumstance of a stroke of the charge exchange valve at variance with the intended stroke. 
   Another, similar valve operating device is furthermore disclosed in DE 42 23 172 C1, wherein the lever that is turned by the cam of a camshaft to achieve a variable stroke—zero stroke to full stroke—is guided by a lever turned by the cam of a camshaft at its free end adjacent to linear contact with a cam serving for stroke adjustment through a slot on a pivot pin affixed to the housing. Even in this guidance method, in case of an operation of the charge exchange valve, the lever is subjected at its pivot point to a rotatory as well as linear component of movement, while the linear component of motion corresponds to the operation of a preliminary cam or a ramp, but otherwise it acts against any increase in the dynamic of the valve operation. 
   The invention is addressed to the problem in the generic valve operating device, to improve a lever cinematically such that it will permit a greater valve operating dynamic in a purely rotational movement or swinging movement. 
   This problem is solved by the invention described and claimed hereinafter by the fact that a circular track arranged on a part of the housing of the internal combustion engine serves as a slide with a radius “R” about the axis of rotation of the wheel of the transfer element of the position-variable support of the lever, while the guidance path of the lever is formed in the area of transition between the idle stroke cam and lifting cam with a ramp set for a valve clearance in the valve operating device. 
   With the invention the advantage is achieved that the pivot point of the lever during the lifting action for a preset valve lift forms an invariable momentary pole and thus any translational component of movement is advantageously prevented. On this basis of the invention the time required for changing the stroke of the charge exchange valve can be reduced to a substantially greater extent, and retarding of the opening and closing sections during partial strokes is largely eliminated. Furthermore, the invention provides a valve operating device of great stiffness, which is furthermore advantageous towards greater valve acceleration. Lastly, the valve operating device of the invention permits an actual zero stroke and an increase of torque by the full opening of the charge exchange valve, combined with great strength at high speeds. 
   In a preferred embodiment of the invention it is proposed that the lever is supported at its end remote from the control track by a wheel which can rotate about an axis, against the circular path or slide and can be fixed each time by the adjusting system such that the wheel&#39;s axis, which can be shifted under control along a path equidistant from the circular orbit, forms the lever&#39;s pivot point serving for the particular variable stroke adjustment. 
   In conjunction with an additional proposal, according to which the circular-path wheel of the lever is to be arranged on needle or roller bearings on a stub shaft affixed to the lever, with the momentary pole or pivot point shifting according to the invention to the axis of the circular-path wheel of the lever, the result is a valve operating device of reduced wear with substantially less friction and high accuracy of operation, while furthermore the energy required for the adjusting system is advantageously reduced. 
   According to an additional preferred embodiment, a wheeled idler arm supported on the side of the housing by a hydraulic valve lifter is provided, while the ramp provided to compensate for the eliminated linear movement component is designed for a substantially constant stroke speed with a maximum stroke exceeding the greatest possible valve clearance. 
   Additional possibilities for the configuration of the transfer element are: formation as a tappet with a wheel, or formation as a lever with a mechanically adjusted valve clearance. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is described with the aid of an embodiment represented in the FIGURE. 
   

   DETAILED DESCRIPTION OF THE DRAWING 
   A valve operating device  1  according to the FIGURE serves to produce the variable valve lift of a charge exchange valve  2  of an internal combustion engine (not shown). The charge exchange valve  2  is one of several identical intake valves of a cylinder of the internal combustion engine. In the valve operating device  1 , the charge exchange valve  2  is in active connection—with the interposition of a transfer element  3  having a wheel  5  turning about an axis  4 —with a control track  6  comprising an idle stroke cam follower  6 ′ and a lifting stroke cam follower  6 ″, which is arranged in the area of the end of a lever  8  operated by a cam  7 ′ of a camshaft  7  for producing the lifting stroke of the charge exchange valve  2 . For a variable stroke adjustment of the charge exchange valve  2 , the lever  8 , which is associated with the cam  7 ′ without free play by means of a spring  9 , is supported along a circular path by a fulcrum  12  whose position can be varied by means of adjusting mechanism  11  and locked in place. 
   In order to achieve a purely rotary or purely rocking movement of the lever  8  about its pivot point  12  with a reduced stroke of the charge exchange valve  2 , an arcuate path  14  arranged on a part  13  of the housing of the internal combustion engine (not shown) as a slide  15  with a radius “R” about the axis of rotation  4  of the wheel  5  of the transfer element  3  for the support at variable positions of the lever  8 . Preferably, at its end remote from the control path the spring-loaded lever  8  thrusts with a wheel  17  rotating about an axis  16  against the arcuate path  14  or slide  15 , and can be held in place by means of a cam  18  of the adjusting system  11  by the action of spring  9  such that the axis  16  of the wheel  17 , which can be displaced along a line  19  equidistant from the circular path  14  or slide  15 , forms the pivot point  12  of lever  8  serving in the particular variable valve lifting action. 
   With the invention it is advantageously brought about that the pivot point  12  of the lever  8  forms an invariable instantaneous center for a preset, reduced stroke and for any stroke during a particular lifting actuation. 
   With the invariable instantaneous center or pivot point  12  the linear movement components of the lever  8  mentioned in the introduction to the description are eliminated. In order in this case to securely prevent any shock originating from a valve action of the valve operating device  1  when the wheel  5  of the transfer element  3  passes from the idle stroke cam  6 ′ to the lifting cam  6 ″ of the control track  6  during a valve lift, the control track  6  of the lever  8  is formed according to the invention in the transition between idle stroke cam  6 ′ and lifting cam  6 ″ with a ramp  20  provided for a valve action in the valve operating device  1 . 
   With this cinematically configured valve operating device  1  an actual zero stroke of the charge exchange valve  2  can be realized; also, the result is a greater reduction of the operating time with a change in the lifting of the charge exchange valve  2 , delayed opening and closing in the case of partial valve operation are eliminated or considerably reduced, so that a greater maximum valve acceleration is advantageously achievable. Furthermore, an improved torque as well as greater torque is also the result at the full load of the internal combustion engine. 
   For the reduction of wear in the valve operating device  1  it is furthermore provided that the guide wheel or circular path wheel  17  of the lever  8  is mounted on needle or roller bearings on a non-rotating stub shaft affixed to the lever  8 . 
   As it can be seen from the FIGURE, the cam follower  10  of the lever  8  is also mounted on needle bearings; the same applies to the wheel  5  of the transfer element  3 . 
   As it can furthermore be seen in the FIGURE, the transfer element  3  is a wheeled idler arm  23  supported on the housing by a hydraulic valve clearance equalizing device  22 , whose wheel  5  cooperates with a control track  6  of the lever  8 , which has a ramp  20  designed substantially for a constant stroke velocity, having a maximum lift exceeding the maximum valve clearance. 
   The transfer element  3  can also conceivably be a valve tappet with a roller, and also a rocker arm with a mechanically adjusted valve clearance. 
   The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations falling within the scope of the appended claims and equivalents thereof.