Abstract:
Valve gears for load-change valves of four-stroke internal combustion engines, in which the load-change valves are closed by spring force, engage a pivot lever moved by a cam for opening a load-change channel. The cam engages an intermediate element that it is additionally moved by the lifting curve of the cam during a different work cycle, and adjusts the pivot lever to open the load-change valve slightly during a different work cycle. The intermediate element is prismatically guided on an element that can pivot in the cylinder head and is adjustable in its position, and engages the cam and the pivot lever, so that the stroke movement of the cam for opening the load-change valve via the pivot lever can be adjusted.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to valve gears for load-change valves of four-stroke internal combustion engines, in which optional opening of the load-change valve during a different work cycle can take place in addition to opening in accordance with the cycle. 
   2. The Prior Art 
   A valve gear of this type, for outlet valves, is described in PCT Application Publication No. WO 03/067067, FIG. 2 and FIG. 4. Outlet valves held in the closed position by spring force are opened according to the cycle, in usual manner, by an outlet cam, by way of a toggle or pivot lever, as well as a pressure plate that acts on the stems of the valves, so that the waste gases can flow out of the cylinder chamber into the waste gas tract via the outlet channel at the end of the expansion cycle and during the movement of the piston to the upper dead point. An intermediate element is articulated onto the toggle or pivot lever, so as to pivot. This element is firmly supported against the toggle or pivot lever by a hydraulic pressure cylinder to which pressure can optionally be applied or, if no pressure is applied to the pressure cylinder, can rotate freely about its articulation point. When pressure is applied to the hydraulic pressure cylinder, the outlet cam stands in engagement with the toggle or pivot lever during the intake process, by way of the intermediate element. This lever is moved exclusively by the highest region of the lifting curve of the outlet cam. The outlet valve is therefore additionally opened during the intake process, but this happens with a significantly lesser time cross-section than during expulsion of waste gas. This is shown in  FIG. 1  of the PCT application mentioned above. 
   By means of the additional opening of the outlet valve during the intake process, waste gas gets into the cylinder from the waste gas tract, by way of the outlet channel, and subsequently mixes with air that is drawn in, or with the fuel/air mixture that is supplied, during intake and compression. In order to achieve a slight time cross-section for returning waste gas during the intake cycle of waste gas, only the highest region of the lifting curve of the outlet cam is utilized. This highest region has a lifting characteristic that is configured to be optimal for the return of waste gas. Such a lifting characteristic forms a compromise with regard to an optimal lifting characteristic for the outlet process of waste gases. 
   It is also disadvantageous that the intermediate element articulated onto the toggle or pivot lever is moved along during all outlet valve movements, i.e., also during the outlet process of the waste gases, without this being functionally necessary. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide a a valve gear of the type stated above, which uses a conventional cam, configured for a specific load change, and which creates a transfer device for the movements brought about by this cam, which device permits sensitive adjustment of different time cross-sections in the case of additional opening during a different work cycle. 
   These and other objects are accomplished by a valve gear for load-change valves of four-stroke internal combustion engines, in which the load-change valves are held in the closed position by means of spring force, and engage a pivot lever moved by a cam, for opening a load-change channel in accordance with the engine cycle. The cam engages an intermediate element, the engagement region of which is positioned on the cam in such a manner that it is additionally moved by the lifting curve of the cam during a different work cycle, and has an adjustable effect on the pivot lever. The load-change valve additionally opens during a different work cycle, but with a lesser time cross-section. The intermediate element is prismatically guided on an element that can pivot in the cylinder head and is adjustable in its position. This element engages the cam and the pivot lever, so that different gear reductions of the stroke movement of the cam for opening the load-change valve with the pivot lever can be adjusted. 
   The use of an intermediate element, which is guided on an element that can pivot in the cylinder head and is adjustable in its position, makes it possible to set different gear reductions of the stroke movement of the cam, for additionally opening the load-change valve, so that the cam can be guided in an optimized manner, exclusively for the load-change process in question—letting out waste gases or drawing in charge. The stroke movement of the inlet or outlet cam is stepped down adjustably, in accordance with the requirements, by the transfer device described above, with the intermediate element and the element that is adjustable in its position, so that the additional opening of the load-change valve, in each instance—intake or outlet valve—can be regulated in a sensitive manner. This is necessary both for returning waste gas into the cylinder during the intake cycle, by way of an outlet valve, and for returning waste gas into the intake tracts, by way of an inlet valve, during the expulsion of waste gas from the cylinder. 
   It is advantageous if during opening of each of the load-change valves, in accordance with the cycle, with large opening paths, only the pivot lever is moved, and the intermediate element remains in its resting position. The intermediate element, with its mass, is only moved by the cam for the additional opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
     In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
       FIG. 1  shows one embodiment of the valve gear according to the invention in a position before opening of the load-change valve, which is an outlet valve here; 
       FIG. 2  shows an embodiment of the valve gear according to the invention in a position with the outlet valve fully open, during expulsion of the waste gases; 
       FIG. 3  shows an embodiment of the valve drive according to the invention in a position during the intake cycle, with the outlet valve slightly open; 
       FIG. 4  shows the valve lifting curve determined by an outlet cam with an embodiment of the valve gear according to the invention for the outlet valve, and the valve lifting curves that can be additionally adjusted during the intake cycle; and 
       FIG. 5  shows the valve lifting curve determined by an inlet cam with an embodiment of the valve gear according to the invention for an inlet valve, during the intake cycle, and the valve lifting curves that can be additionally adjusted during the cycle, for expulsion of the waste gases. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings,  FIG. 1  shows a side view of the elements of one embodiment of the valve gear according to the invention, with a view in the direction of the progression of the camshaft axis. A camshaft  1 , driven by the crankshaft, if necessary by way of an angle adjustment device, is mounted to rotate in the cylinder head ZK, fixed in place, and turns in the clockwise direction in all of the views. Camshaft  1  has cams  11  whose lifting curve and angular position relative to the crankshaft are adapted to letting out and expelling waste gases. Accordingly, load-change valve  2  activated by the valve gear is an outlet valve. 
   A guided stroke transfer arrangement  3 , fixed in place, having a pivot lever  30  is assigned to load-change valve  2  disposed in cylinder head ZK, in each instance, which valve closes by means of spring force. Only the end part of the valve stem is shown in  FIG. 1 . The end surface of the valve stem rests against a play equalization element  33  disposed in pivot lever  30 . Pivot lever  30  is constantly forced against the running surface of cam  11 , with its roller  31 , without play, by means of the force of said element. Roller  31  mounted on pivot lever  30  therefore forms a first engagement surface on pivot lever  30 . 
   Pivot lever  30  is mounted adjustably on an axle  34  guided in cylinder head ZK, with the interposition of an eccentric bushing  35 . An intermediate element  5  is positioned relative to cam  11  with a roller  53  mounted on it, in such a manner that roller  53  comes into engagement with the lifting curve of cam  11  during the intake process, in other words only after expulsion of the waste gases. By means of this arrangement, intermediate element  5  is moved by cam  11  exclusively during the intake process. An element  40  that is fixed in place in cylinder head ZK, but can be adjusted in its position about a rigidly positioned pivot axle, and intermediate element  5  together form a transfer device  6 , which is actually known (see  FIGS. 2 and 3 ) for differently adjustable gear reduction of the stroke movement of cam  11  during transfer to the pivot lever  30  and load-change valve  2 . 
   Intermediate element  5  engages element  40 , which is changeable in its position, in a non-positive lock, on the controlling cam segment  42  of element  40 , by way of roller  54  mounted on it, as well as with line contact on a supporting cam segment  41 , by slide supports  55 . The outer contour of the supporting cam segments  41  forms an arc about the pivot axle of element  40  in cylinder head ZK. This arrangement forms a prismatic support of intermediate element  5  on element  40  that is changeable in its position, and thereby assures guidance of intermediate element  5  in every phase of a movement brought about by cam  11 . 
   Under the effect of force F of a spiral spring  51  counter-mounted and guided on cylinder head ZK in a fixed position, intermediate element  5  is constantly forced both against changeable element  40  with its roller  54  and its slide supports  55 , and against cam  11  with its roller  53 , and held in engagement. 
   Intermediate element  5  furthermore has an outer contour  52  that engages a second roller  32  on pivot lever  30 . Roller  32  therefore forms a second engagement surface on pivot lever  30 , which comes into engagement exclusively for opening load-change valve  2  during the intake process, see  FIG. 3 . 
   By means of transfer device  6 , sensitively controlled opening of load-change valve  2  with lesser time cross-sections can be achieved, for returning waste gas from the waste gas tract into the cylinder, during the intake process. 
   Fundamentally, the structure of transfer device  6 —see FIGS.  2  and  3 —and its function for varying the valve stroke is already previously known from German Patent No. DE 202 20 138 U1, the disclosure of which is herein incorporated by reference. 
   Eccentric bushing  35  disposed between axle  34 , which is fixed in place, and the bearing bore of pivot lever  30 , adjusts the engagement play between outer contour  52  on intermediate element  5  and roller  32  on pivot lever  30 . The eccentric bushing  35  is clamped in place in the bearing bore of pivot lever  30  after the aforementioned engagement play has been adjusted, by means of a clamp screw arrangement  36  in pivot lever  30 . 
   The device according to the invention functions as follows: 
   In  FIG. 1 , load-change valve  2  is closed, roller  31  of pivot lever  30  and roller  53  on intermediate element  5  stand in engagement with the base circle of cam  11 . When cam  11  turns further, from the aforementioned position, in the clockwise direction, roller  31  is first constantly forced in the direction of valve opening by its lifting, until the outermost cam contour has been reached, see  FIG. 2 , and load-change valve  2  is always opened with a constant stroke. Roller  32  on pivot lever  30  moves away from its engagement region on outer contour  52  of intermediate element  5 , which does not move, when load-change valve  2  is fully open, by a distance segment S, because roller  53  of element  5  runs on the base circle of cam  11  at this point in time. 
   According to the functional position shown in  FIG. 2 , load-change valve  2  is subsequently closed by means of a spring force, whereby roller  31  of pivot lever  30  comes back to the base circle of cam  11 . With this, the engagement play that is adjusted by the eccentric bushing  35 , between outer contour  52  on the intermediate element  5  and roller  32  on pivot lever  30 , is also present again. As cam  11  rotates further, its lifting moves roller  53  and therefore intermediate element  5 , until the outermost cam contour is reached. Depending on the position of element  40 , which is changeable in its position, intermediate element  5  is forced, to a greater or lesser degree, in the direction of valve opening, by the controlling cam segment  42 , by way of its roller  54  with its outer contour  52 , against roller  32  of pivot lever  30 , see  FIG. 3 . 
   In  FIG. 3 , a slight opening of load-change valve  2  for waste gas return is adjusted, as can be seen from distance segment A, lifting roller  31  of pivot lever  30  from the base circle of cam  11 . If adjustable element  40  were moved further out of the position shown in  FIG. 3 , in the counter-clockwise direction, load-change valve  2  would be opened more than in  FIG. 3 , because intermediate element  5 , with its roller  54 , would be pushed more onto controlling cam segment  42 , and therefore the intermediate element  5 , with its outer contour  52 , would also be displaced more against roller  32  of pivot lever  30 . The distance segment A would then be greater than that in  FIG. 3 . 
   After the highest lifting of cam  11  on roller  53  has gone by, the force F of spiral spring  51  and the return force of the valve spring forces pivot lever  30  and intermediate element  5  back in the direction of the base circle of cam  11 , by way of play equalization element  33 . Finally, roller  31  mounted on pivot lever  30  comes back into non-positive-lock engagement with the base circle of cam  11 . 
     FIG. 4  shows valve lifting curves that can be achieved with the valve gear according to the invention, for a load-change valve  2 , which is an outlet valve, in this case, with their location in the cycle regions of a four-stroke engine. Cam  11  always opens load-change valve  2  at a constant stroke, at the end of the expansion cycle and during expulsion, see ÖA. Adjustable opening of load-change valve  2 , see group of curves ÖAR, can take place even during intake, by way of intermediate element  5  of transfer device  4 . Return of waste gases from the waste gas tract into the cylinder is achieved in this way. If waste gas return is undesirable, opening of load-change valve  2  is prevented by transfer device  6 , it remains in the closed state. 
   In  FIG. 5 , the valve lifting curves that can be achieved with the valve gear according to the invention for a load-change valve acting as an inlet valve are shown. Cam  11  is configured as an inlet cam, and camshaft  1  turns counter-clockwise, in contrast to the embodiment described above. During the cycle—expulsion of waste gas—lifting of cam  11  reaches roller  53  and displaces intermediate element  5  until the outermost cam contour is reached. Depending on the position of element  40  that is changeable in position, intermediate element  5  is forced in the direction of opening, to a greater or lesser degree, by means of controlling cam section  42 , by way of its roller  54  with its outer contour  52 , against roller  32  of pivot lever  30 , see  FIG. 3 , so that the lifting curves ÖER shown in  FIG. 5  can be adjusted for the inlet valve. Thus, the return of waste gas into the intake tract, by way of the inlet valve, during expulsion of waste gas from the cylinder, can be regulated in a sensitive manner. As camshaft  1  turns further, cam  11  engages roller  31  on pivot lever  30 —see FIG.  2 —and opens load-change valve  2 , which is acting as an inlet valve, in usual manner, before the beginning of the intake cycle until the beginning of the compression cycle, always at a constant stroke, see ÖE in  FIG. 5 . 
   Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 
   REFERENCE SYMBOLS 
   
       
         1  camshaft 
         11  cam (inlet or outlet cam) 
         2  load-change valve (inlet or outlet cam) 
         3  lift transfer arrangement 
         30  pivot lever 
         31  roller 
         32  roller 
         33  play equalization element 
         34  axle for mounting  30   
         35  eccentric bushing 
         36  clamp screw arrangement in  30  for  35   
         4  transfer device 
         40  element that is changeable in its position, can pivot 
         41  supporting cam segment 
         42  controlling cam segment 
         5  intermediate element 
         51  spiral spring 
         52  outer contour 
         53  roller 
         54  roller 
         55  slide support 
         6  transfer device for the additional opening of  2  brought about by  11   
       A distance segment 
       F force of  51  that engages at  5  and holds  5  against  4  and  11  with a non-positive lock 
       ÖA opening of  2  (outlet valve) for letting out and expelling waste gas 
       ÖAR group of curves during opening of  2  (outlet valve) for returning waste gas during the intake cycle 
       ÖE opening of  2  (inlet valve) for intake 
       ÖER lifting curves during opening of  2  (inlet valve) for returning waste gas into the intake cycle during expulsion of waste gas 
       S distance segment 
       ZK cylinder head