Abstract:
A valve drive for charge-cycling valves of internal combustion engines, which are held in the closed position by means of spring force, and can optionally be activated by a main cam or additionally by a secondary cam of a camshaft, in which connection the main cam with its elevation curve and angle setting is adapted to the crankshaft of a charge-cycling process to be controlled, and the secondary cam operates separately from the main cam. The drive variably controls an additional opening procedure of a charge-cycling valve, separate from the charge-cycling stroke to be controlled directly, in order to sensitively regulate the exhaust gas feed-back in this manner. The drive has two engagement surfaces for introducing movements on a pivot lever mounted on the cylinder head, which activates at least one charge-cycling valve. The first engagement surface on the pivot lever engages the main cam and the second engagement surface on the pivot lever contacts a transfer device for variable adjustment of the valve lift, driven by the second cam.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to valve drives for charge-cycling valves of internal combustion engines.  
         [0003]     2. The Prior Art  
         [0004]     A valve drive of this type, for outlet valves of four-stroke internal combustion engines is described in French Patent No. FR 976.076, in which an outlet valve held in the closed position by a spring force is optionally activated by a first or a second cam, with different lifts of a camshaft. The two cams form an axially displaceable unit that is mounted on the camshaft so as to rotate with it, but to be displaceable. This unit can be displaced into two different positions by a switching fork.  
         [0005]     The first cam is adapted to a charge-cycling process to be controlled, with its elevation curve and angle position relative to the crankshaft, and the second cam is active in a different stroke region than the first cam.  
         [0006]     In the first position, the first cam is in engagement with the tappet of the valve; in the second position, both the first and the second cam are in engagement with the tappet. The first cam constantly controls the usual opening of the outlet valve after expansion and during expulsion of the combustion gases. The second cam, which can be alternatively placed into a position that is ineffective or effective for the outlet valve, opens the outlet valve, in its effective position, in addition to its usual opening during the intake and/or compression stroke. In this way, the exhaust gas also goes into the cylinder, in addition to the charge that was drawn in, in the case of intake throttling with a low fill volume of the cylinder, so that a greater compression is achieved.  
         [0007]     A valve drive for outlet valves of four-stroke internal combustion engines is described in Japanese Patent No. JP 03-202 603, with an outlet cam that has a second elevation and that can be lowered. In its active, outermost position, this elevation opens the outlet valve in addition to its usual opening during the intake and/or compression stroke. In the lowered position, the second elevation is below or at the position of the cam basic circle, and is therefore ineffective.  
         [0008]     It is disadvantageous in these embodiments that due to the alternatively effective or ineffective switching of the second cam, the exhaust gas to be introduced in addition to the charge that is drawn in during the intake and/or compression stroke cannot be precisely metered.  
         [0009]     A variable valve drive is described in German Patent No. DE 101 56 309 A1, in which a cam with only one elevation is in engagement with a cup tappet, and an additional hydraulic activation device is disposed in the cup tappet. With this activation device, which is supplied and controlled by an additional pressure supply unit, additional opening outside the region of engagement of the cam elevation is possible and an enlargement of the valve opening beyond the opening process of the valve by the lift of the cam can be achieved.  
         [0010]     This variable valve drive for outlet valves is used for implementing an exhaust gas feed-back by an additional, multiple opening of the outlet valves outside of the stroke for expulsion of exhaust gas during the intake and/or compression stroke.  
         [0011]     German Patent No. DE 44 24 802 C1 describes a process in which an inlet valve is opened during the stroke for expulsion of exhaust gas, in order to bring about an exhaust gas feed-back from the cylinder into the intake system. The inlet valve is activated by a cam having different elevations. For variable activation of the valve for the additional opening process, independent of the lift of the related cam, the hydraulic cushion of the hydraulic valve place adjustment is utilized.  
         [0012]     It is a disadvantage of the two valve drives described above that in order to control the additional opening of the charge-cycling valves, a separate pressure system with a control device synchronized with the crankshaft is required.  
         [0013]     A method for operating internal combustion engines with variable gas change control times is described in German Patent No. DE 199 05 364 C1. For a direct feed-back of exhaust gas during the intake and compression stroke, the opening time of the outlet valve extends from the end of the expansion stroke over the expulsion stroke to half of the intake stroke, and greater overlap of the valve opening of the outlet and inlet valve occurs.  
         [0014]     To the extent that charge-cycling valves are discussed below, these can be both inlet valves and outlet valves.  
       SUMMARY OF THE INVENTION  
       [0015]     It is an object of the invention to variably control an additional opening process of a charge-cycling valve, using a mechanical valve drive, which is separate from the charge-cycling stroke to be controlled directly, in order to regulate the exhaust gas feed-back in sensitive manner.  
         [0016]     This object is accomplished by a valve drive for charge-cycling valves of internal combustion engines, which are held in the closed position by spring force and can optionally be activated by a main cam or additionally by a secondary cam of a camshaft. The connection of the main cam with its elevation curve and angle setting is adapted to the crankshaft of a charge-cycling process to be controlled. The secondary cam operates independently of the main cam. There are two engagement surfaces for introducing movements. The engagement surfaces are disposed, in different positions, on a pivot lever mounted on the cylinder head, which activates at least one charge-cycling valve. The first engagement surface on the pivot lever engages the main cam. The second engagement surface on the pivot lever contacts a transfer device for variable adjustment of the valve lift, driven by the second cam.  
         [0017]     The use of a pivot lever to activate one or two charge-cycling valves, in an embodiment according to the invention, having two engagement surfaces for the introduction of lifting movements, allows direct engagement with a first main cam that allows for an opening and closing of one or two valve(s), respectively, for a charge cycle, e.g. intake of fresh gas or expulsion of exhaust gas, and an engagement with a transfer device driven by a second cam, for a variable adjustment of the valve lift for feed-back of exhaust gas into the cylinder chamber or also into the intake pipe.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     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.  
         [0019]     In the drawings, wherein similar reference characters denote similar elements throughout the several views:  
         [0020]      FIG. 1  shows a side view of the elements of a valve drive according to one embodiment of the invention, with a view in the direction of the progression of the camshaft axis;  
         [0021]      FIG. 2  shows a view from above onto the valve drive according to an embodiment of the invention;  
         [0022]      FIG. 3  shows a perspective view of a valve drive according to an embodiment of the invention;  
         [0023]      FIG. 4  shows a perspective view of a second embodiment of a valve drive according to the invention, having a two-part pivot lever;  
         [0024]      FIG. 5  shows a view from above, onto an embodiment of the valve drive according to  FIG. 4 ;  
         [0025]      FIG. 6  shows valve elevation curves with valve drives according to the invention, for inlet valves and  
         [0026]      FIG. 7  shows valve elevation curves with valve drives according to the invention, for outlet valves. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]      FIG. 1  shows a side view of the elements of a valve drive according to one embodiment of 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, is mounted in the cylinder head ZK, so as to rotate, with a fixed axis position, and has a fixed position relative to charge-cycling valves  2  and a lift transfer arrangement  3  assigned to them. Lift transfer arrangement  3 , guided in a fixed position, is assigned to charge-cycling valves  2  that are disposed in cylinder head ZK and close by means of spring force. It is formed by a pivot lever  30  mounted on cylinder head ZK and provided with a play equalization element  33 . A main cam  11  of camshaft  1  is in engagement with pivot lever  30  by way of a roll  31  mounted on pivot lever  30 , which roll forms the first engagement surface on pivot lever  30 .  
         [0028]     Camshaft  1 , in addition to the main cam  11  whose elevation curve and angle position relative to the crankshaft is adapted to a charge-cycling process to be controlled, furthermore has a second cam  12  that is active in a different stroke region from main cam  11 .  
         [0029]     The second engagement surface on the pivot lever  30  forms a roll  32  that is mounted on the lever. It stands in engagement with a transfer device  4  driven by second cam  12 , for movements brought about by second cam  12 , for variably adjusting the valve lift. Transfer device  4  has an element  40  whose position can be changed and is disposed in a fixed location in the cylinder head ZK so as to pivot about the pivot axis A 4 , which is in a fixed position, to adjust the valve lift. It forms an adjustable counter-bearing for an intermediate member  5  that is supported on it and is guided during its displacement in this manner. The intermediate member  5  stands in engagement with element  40 , which can change its position, with a non-positive lock, by way of roll  54  mounted, on its control cam  42  as well as with slide supports  55  on the support cams  41  disposed on both sides of the control cam  42 . Support cams  41  are radially offset towards the rear, with a non-positive lock. The outer contour of support cams  41  is formed by an arc about pivot axis A 4  (see  FIG. 2  in this regard). An axial guidance of intermediate member  5  is achieved by support cams  41  on both sides that are radially offset towards the rear, as compared with control cam  42 . This arrangement results in a prismatic support of intermediate member  5  on element  40  that is changeable in its position, in the case of every position during the lift movement.  
         [0030]     Furthermore, intermediate member  5  is in engagement with second cam  12  of camshaft  1 , with the roll  53  mounted on it, and furthermore with a roll  32  of lift transfer arrangement  3  assigned to charge-cycling valves  2 , by way of its outer contour  52 .  
         [0031]     Intermediate member  5  is held in engagement with second cam  12  and changeable element  40 , with a non-positive lock, under the effect of the force of a spring F. For this purpose, spring F is supported and guided on intermediate member  5  in a sliding manner in the region of roll  53 , and fixed in place on the cylinder head ZK (not shown).  
         [0032]      FIG. 3  shows a perspective view of the valve drive according to the invention, in connection with all the charge-cycling valves assigned to the cylinder, and their drive mechanisms, as well as an injection nozzle disposed in the center of the combustion chamber.  
         [0033]      FIG. 4  shows a second embodiment of a valve drive according to the invention, with a two-part pivot lever, in a perspective view.  FIG. 5  shows this valve drive from above. In contrast to the first embodiment, the pivot lever  30  is configured in two parts and consists of a main pivot arm  301  and a secondary pivot arm  302 , in each instance, whereby these two pivot arms  301 ,  302  are articulated independent of one another, but with the same axis, and are in engagement with one of the charge-cycling valves  2 , in each instance.  
         [0034]     Main pivot arm  301  has roll  31  as an engagement surface for the first main cam  11 , on the one hand, and a driver  303  that acts exclusively in the direction of the open valve and stands in engagement with the secondary pivot arm  302 , on the other hand. Secondary pivot arm  302  additionally stands in engagement with transfer device  4  driven by second cam  12 , by way of roll  32  that is mounted on it. Transfer device  4  is the same as the one in the valve drive described according to FIGS.  1  to  3 .  
         [0035]     This second embodiment of a valve drive has the following fundamental functional behavior: The movements brought about by main cam  11  are constantly transferred to both charge-cycling valves  2 . In contrast, the movements brought about by second cam  12  only become effective at charge-cycling valve  2  assigned to the secondary pivot arm  302 , as a function of the setting of the transfer device  4 .  
         [0036]     Fundamentally, the structure of transfer device  4  and its function for varying the valve lift are already known from DE 202 20 138 U1, and need not be described in detail here.  
         [0037]     The embodiment shown in  FIGS. 1-3  functions as follows: The charge-cycling valves  2  are closed. Rolls  31  and  53 , in each instance, are in engagement with the basic circle of the main cam  11  and second cam  12 , respectively. In case of a further rotation from this position, in a clockwise direction, roll  53  is first constantly forced in the direction of the opening of the valve, from the elevation of second cam  12  until the outermost cam contour is reached, and subsequently valve  2  is closed by spring force, not shown. During the movement progression, intermediate member  5  glides on support cam  41  and control cam  42 , with line contact, and in the direction of the longitudinal expanse, by way of the roll  32  of lift transfer system  3 . By means of the structure and the set angle position of element  40  with the control cam  42 , an adjustable, variable opening of the two charge-cycling valves  2  is possible. In case of further rotation, main cam  11  moves pivot lever  30 , by way of roll  31 , which lever always opens the two charge-cycling valves  2  at a constant lift, in usual manner.  
         [0038]     With the embodiment shown in  FIGS. 4 and 5 , the movements brought about by the main cam  11  are always transferred to both charge-cycling valves  2 . In contrast, movements brought about by second cam  12  only become effective at the charge-cycling valve  2  assigned to secondary pivot arm  302 , as a function of the setting of transfer device  4 .  
         [0039]     According to  FIGS. 4 and 5 , the charge-cycling valves  2  of the valve drive are closed. Rolls  31  and  53  are in engagement with the basic circle of main cam  11  or second cam  12 , respectively, in each instance. In case of further rotation of the camshaft  1  in the clockwise direction, from the position shown in the aforementioned figures, roll  53  is first constantly forced in the direction of the opening of the valve, from the elevation of second cam  12  until the outermost cam contour is reached, whereby charge-cycling valve  2  assigned to secondary pivot arm  302  is opened as a function of transfer device  4 , and subsequently closed by means of spring force, not shown.  
         [0040]     With the structure and the set angle position of the element  40  with control cam  42 , in each instance, adjustable, variable opening of charge-cycling valve  2  activated by secondary pivot lever  302 , in each instance, is possible. During this process, main pivot arm  301  continues to support itself on the basic circle of main cam  11 . Charge-cycling valve  2  assigned to the main pivot arm  301  remains closed.  
         [0041]     In case of further rotation, main cam  11  moves main pivot arm  301  with driver  303 , which is in engagement with secondary pivot arm  302  in the direction of the open valve, by way of the roll  31 . In usual manner, the two charge-cycling valves  2  are always opened by the main cam  11  at a constant lift.  
         [0042]     Possible valve elevation curves that can be implemented with the valve drives according to the invention are shown in  FIGS. 6 and 7  and will be explained below.  
         [0043]      FIG. 6  shows valve elevation curves of inlet valves with the location in the stroke regions of four-stroke engines that can be implemented with valve drives according to the invention. In this case, the charge-cycling valves  2  are inlet valves.  
         [0044]     With the embodiment according to  FIG. 3 , both inlet valves are always activated synchronously. Main cam  11  always opens the two inlet valves at a constant lift during intake, see Ö 11 .  
         [0045]     The adjustable opening of the two inlet valves takes place by way of the second cam  12  and transfer device  4 , see curve group Ö 12 , even during expulsion of the exhaust gases. In this way, exhaust gas feed-back from the cylinder into the intake tract is achieved. If such exhaust gas feed-back is not desired, opening is prevented by second cam  12 , by means of transfer device  4 . Both inlet valves remain in the closed state.  
         [0046]     In the case of an embodiment of the valve drive according to  FIG. 4  or  5 , the two inlet valves are always opened at a constant lift during intake, by main cam  11 , see Ö 11 . Adjustable opening only of the inlet valve activated by secondary pivot arm  302  takes place exclusively by way of second cam  12  and transfer device  4 , in accordance with the curve group Ö 12  shown in  FIG. 6 . The inlet valve activated by main pivot arm  301  remains closed. With this embodiment, in which only one of the inlet valves is effective for exhaust gas feed-back, more precise metering of the amount of exhaust gas fed back can be achieved.  
         [0047]      FIG. 7  shows valve elevation curves of outlet valves with their location in the stroke regions of four-stroke engines that can be implemented with valve drives according to the invention. In this case, the charge-cycling valves  2  are outlet valves.  
         [0048]     When using an embodiment of the valve drive according to  FIG. 3 , the two outlet valves are always activated synchronously. Main cam  11  opens both outlet valves at the end of the expansion stroke, and during expulsion, always at a constant lift, see Ö 11 . The adjustable opening of the two outlet valves, see curve group Ö 12 , can take place by way of second cam  12  and the transfer device  4 , even during the beginning of compression, but after closing of the inlet valves. In this way, exhaust gas feed-back from the exhaust gas tract into the cylinder is achieved.  
         [0049]     If such exhaust gas feed-back is not desired, opening of the outlet valves is prevented by second cam  12 , by means of transfer device  4 . Both outlet valves remain in the closed state.  
         [0050]     When using an embodiment of the valve drive according to  FIG. 4  or  5 , both outlet valves are opened by main cam  11  at the end of the expansion stroke and during expulsion, always at a constant lift, see Ö 11 .  
         [0051]     Adjustable opening only of the outlet valve activated by secondary pivot arm  302  takes place exclusively by way of second cam  12  and transfer device  4 , corresponding to curve group Ö 12  shown in  FIG. 7 . The outlet valve activated by the main pivot arm  301  remains closed.  
         [0052]     With this embodiment, in which only one of the outlet valves is active for exhaust gas feed-back, it is possible to achieve more precise metering of the amount of exhaust gas fed back, if necessary even an influence on the charge movements in the cylinder chamber.  
         [0053]     If no exhaust gas feed-back is desired, opening of the outlet valve is prevented by second cam  12 , by means of the transfer device  4 .  
         [0054]     To achieve several lifts, second cam  12  can have several elevations that are effective separate from main cam  11 . If the elevations on second cam  12  are different, it is possible to adjust the size of the additional lifts depending on the position of changeable element  40 , in each instance and, for example, to suppress lifts that result from slight elevations on second cam  12 .  
         [0055]     In the latter case, not all the elevations on second cam  12  become effective for opening charge-cycling valves. However, such an embodiment is not shown in any of the Figures.  
         [0056]     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  
       [0000]    
       
           1  camshaft  
           11  main cam  
           12  second cam  
           2  charge-cycling valve  
           3  lift transfer arrangement  
           30  pivot lever  
           31  roll  
           32  roll  
           33  play equalization element  
           301  main pivot arm  301   
           302  secondary pivot arm  
           303  driver on  301   
           4  transfer device for movements brought about by the second cam  12   
           40  element, changeable in its position, pivotable  
           41  support cam  
           42  control cam  
           5  intermediate member  
           52  outer contour  
           53  roll  
           54  roll  
           55  slide support  
          F spring whose force engages at  5  and places [it] against  4  and  12   
          ZK cylinder head  
          Ö 11  opening of valves  2  by means of the main cam  11   
          Ö 12  adjustable opening of valves  2  by the second cam  12