Abstract:
A valve actuation device may comprise a camshaft including first and second cams, the second cam having a larger lobe than the first cam. A valve lever includes a first follower component or surface adapted to follow the first cam and a second follower component or surface adapted to follow the second cam. The second follower component or surface may be mounted on or defined by an eccentrically-disposed device, which is rotatable relative to the first follower component or surface. When the rotatability of the second follower component or surface is locked by a latching device, the second follower surface translates the contour of the second cam into actuation of an engine valve and, when the second follower component or surface is freely rotatable, the first follower surface translates the contour of the first cam into actuation of the engine valve.

Description:
CROSS-REFERENCE 
     This application is the U.S. national stage filing of International Application No. PCT/EP2006/007365 filed Jul. 26, 2006, which claims priority to German patent application nos. 10 2005 037 391.7 filed Aug. 8, 2005 and 10 2005 039 368.3 filed Aug. 19, 2005. 
     TECHNICAL FIELD 
     The invention relates to a switchable valve actuating mechanism, as is used, e.g., in reciprocating-piston internal combustion engines for switching the valve timing of an intake valve. 
     Switchable valve actuating mechanisms are in use in a variety of ways and serve to adapt the valve timing to differing operating conditions in order to favorably influence the power development, the torque behavior and the exhaust gas ratio. 
     A switchable valve actuating mechanism according to the preamble of claim  1  is known from DE 102 30 108 B4. With this apparatus for adjusting the stroke length of a valve actuated by a camshaft, a bearing pin is rotatably borne on the valve lever, which bearing pin includes two bearing segments that are eccentric relative to its rotational axis; a cam roller that follows one of the cams of the camshaft is borne on each bearing segment. The bearing pin is connected with a friction disk so as to rotate therewith; the outer circumference of the friction disk is in frictional engagement with a circumferential surface of the camshaft for rotating the bearing pin. The rotatability of the friction disk is lockable in different rotational positions. 
     SUMMARY 
     The object underlying the invention is to provide a switchable valve actuating mechanism, which operates with low friction in a compact construction and makes possible a reliable switching of the valve actuation from one cam of a camshaft to another cam of the camshaft. 
     In one aspect of the present teachings, a switchable valve actuation mechanism includes a camshaft having at least one first cam and one second cam that is higher than the first cam. A valve lever is supported on an engine-mounted component and on the to-be-actuated valve. The valve lever includes a first follower component adapted to follow the first cam and a second follower component adapted to follow the second cam. The second follower component is mounted on an eccentric device, which is rotatably borne on and/or in the valve lever. A latching mechanism is adapted to latch or lock the rotatability of the eccentric device. Preferably, when the rotatability of the eccentric device is latched, the second follower component translates the contour of the second cam into a corresponding actuation of the valve. On the other hand, when the eccentric device is freely rotatable, the first follower component translates the contour of the first cam into a corresponding actuation of the valve. 
     With the inventive valve actuating mechanism, the first follower component follows the contour of the first cam when the eccentric device is freely rotatability, so that the eccentric device must be rotated only by a predetermined rotational amount or angle in order to be positioned to follow the second follower component, at which position the rotatability of the eccentric device is latched. Additional components are not required to rotate the eccentric device. 
     In a further aspect of the present teachings, the valve lever may include two spaced-apart side parts. An opening may extend through the spaced-apart side parts and may be dimensioned to bear the eccentric device. The first follower component may include a follower surface disposed concentrically to the rotational axis of the eccentric device. The follower surface is preferably accessible between the side parts for abutment on the first cam. 
     The first follower component is preferably a roller that is borne concentrically to the rotational axis of the eccentric device. The eccentric device may be borne in a bushing that is inserted in the opening of the side parts. The roller preferably forms the first follower component and is borne on or in the bushing. 
     The second follower element is also preferably a roller that is borne on a bearing pin. Preferably, the bearing pin protrudes laterally from the eccentric device and is radially displaced from the rotational axis of the eccentric device. 
     In further aspects of the present teachings, the movability of the eccentric device into and out of its latchable rotational position may be achieved in a particularly simple manner. For example, a spring may be supported between the eccentric device and the valve lever. The spring preferably biases the eccentric device in the direction of abutment of the second follower component on the second cam. In addition or in the alternative, the latching mechanism may include a connecting lever connected with the eccentric device so as to rotate therewith. The position of the connecting lever is preferably latchable relative to the valve lever when the second follower component abuts on the base circle of the second cam. In addition or in the alternative, a locking component may be mounted on the valve lever. The locking component may be capable of reciprocating between a first position, in which the pivotability of the connecting lever is locked, and a second position, in which the connecting lever is permitted to pivot. In addition or in the alternative, the locking component may be formed as a shift pin that is displaceable against the biasing force of a spring by applying a hydraulic pressure to the shift pin. In addition or in the alternative, the engine-mounted component, on which the valve lever is supported, may be formed as a hydraulic valve play-compensating element, which is adapted to bias the shift pin using hydraulic pressure. 
     In a further aspect of the present teachings, a second follower component may be provided on each side of the eccentric device. In this case, the second follower components interact with respective second cams, thereby symmetrically depressing or actuating the valve lever. 
     The invention, which can be utilized for substantially all types of camshaft-actuated valves and which allows a switching between two differing opening curves, of which one can be a null-actuation, is explained in an exemplary manner in the following with the assistance of schematic drawings and with further details. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the Figures: 
         FIG. 1  shows a perspective overall view of a valve actuating mechanism, 
         FIG. 2  shows parts of the valve actuating mechanism of  FIG. 1  in exploded illustration, 
         FIG. 3  shows a cross-section through a locking mechanism, 
         FIGS. 4 and 5  show different perspective views of a valve lever with accompanying components, 
         FIG. 6  shows a perspective view of a connecting lever, 
         FIGS. 7 to 9  show different perspective views similar to  FIG. 1  in different functional states, and 
         FIGS. 10 to 13  show side views of  4  embodiments, differing with respect to a spring device, of the valve actuating mechanism, each in two different positions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A charge exchanging valve  2 , for example an intake valve of an internal combustion engine, according to the Figures is actuated by a camshaft  4  with a valve lever  6  disposed therebetween. One end of the valve lever  6  is supported on a known hydraulic valve play-compensating element  8  and the other end is supported on the shaft of the valve  2 ; the valve lever  6  abuts on cams  12  and  14 , respectively, between the ends of the valve lever  6  in a manner that will be further discussed below. As is apparent, a middle first cam  12  is formed with a smaller lobe than second, side cams  14 , which accommodate the first cam  12  therebetween. A valve closing spring is denoted with  16 . The hydraulic valve play-compensating element  8  acts so that the valve lever  6  is in play-free abutment on at least one of the cams and on the shaft of the valve, respectively. 
       FIG. 2  shows the valve lever  6  and the components mounted thereon in exploded perspective illustration. 
     The valve lever  6  includes two end portions  18  and  20 , which are connected to each other via spaced-apart side parts  22 . A bushing-accommodation opening  24  penetrates through the side parts  22 ; a bushing  26  is insertable in the opening  24 . 
     The end portion  18 , which abuts on the valve play-compensating element  8 , has a hollow interior and includes a side opening  28 . 
     As shown in  FIG. 2 , a stop  30  is formed on the lower, left side of the end portion  18 . An eccentric device  32  is insertable into the bushing  26 ; cylindrical roller elements  34  are disposed along the eccentric device  32  so that the eccentric device  32  is rotatable in the bushing  26 . 
     Bearing pins  36  project from the side surfaces of the eccentric device  32  eccentrically to the rotational axis of the eccentric device  32 , which rotational axis is coaxial to the axis of the bushing  26  in the assembled state; the bearing pins  36  are coaxially aligned. 
     A follower ring and/or a follower roller  38  is insertable in a slot  37  formed between the side parts  22  of the valve lever  6 ; the inner side of the follower roller  38  is provided with not-illustrated roller elements; the follower roller  38  is borne by these roller elements in a state slidable on the bushing  26 . 
     A hole  40  of a connecting lever  42  is slidable onto the left bearing pin  36  according to  FIG. 2 ; the connecting lever  42  includes a lateral projection  46  ( FIG. 6 ) formed with a slot  44 , which projection  46  fits in a through-opening  48  of the eccentric device  32 . One end portion of the connecting lever  42  includes a recess  50  and an abutment surface  52 . 
     A torsion spring  54  is insertable into the through-opening  48 ; one end leg (not illustrated) of the torsion spring  54  can engage in the slot  44  of the connecting lever and the other end leg  55  of the torsion spring  54  can be supported on a protrusion  56  of the valve lever  6  (cf.  FIGS. 4 ,  8  and  9 ). 
     Follower rings and/or follower rollers  58  can be borne on the bearing pins  36  via roller elements provided in the follower rollers  58 . The follower rollers  58  are advantageously disposed on the bearing pins  36  between washers  60 , wherein the outer washers  60  are advantageously formed as locking rings that axially secure the follower rollers  58  on the bearing pins  36 . 
     The end portion  18  of the valve lever  6  includes a cylindrical cavity  62  that ends in the opening  28  at the left according to  FIG. 3  and merges in a bore  64  to the right. 
     A piston  66 , which has a U-shaped cross-section as a whole, is inserted in the cavity  62 ; the piston  66  is held by a pin  68  that penetrates through the piston body and is screwed into the bore  64 . A spring  70  is supported between the pin  68  and the piston  66 . A portion of the cavity  62 , which is located to the right of the piston body in  FIG. 3 , is connected with a recess  74  via a passage  72 ; the valve lever  6  abuts on the valve play-compensating element  8  via the recess  74 . The passage  72  and thus the piston  66  are biased with hydraulic pressure from the valve play-compensating element  8 . 
     The components illustrated in  FIG. 2  are assembled, for example, as follows: 
     The follower roller  38  is introduced into the slot  37  of the valve lever  6 . The bushing  26  is then inserted, so that the bushing is held in the opening  24  and the follower roller  38  is rotatably borne on the bushing  26 . The eccentric device  32  is inserted into the bushing  26 , so that the eccentric device  32  is rotatable as a whole about the axis of the bushing  26 . The torsion spring  54  is inserted into the through-opening  48  of the eccentric device  32 . Then, the connecting lever  42  and one follower roller  58  are pushed from one side onto one bearing pin  36  and the other follower roller  58  is pushed onto the other bearing pin  36 , wherein washers are disposed in between if desired. The follower rollers  58  are secured on the bearing pins  36  by lock washers. 
     The piston  66  is inserted into the opening  28  and is secured by the pin  68 ; the spring  70  is disposed therebetween. 
     The resulting assembly is disposed on the valve play-compensating element and the shaft of the valve  2 . The legs of the torsion spring  54  are mounted such that the connecting lever  42  and the eccentric device  32 , which is connected with the connecting lever  42  so as to rotate therewith, respectively, are pretensioned for one rotation in the clockwise direction, i.e. the follower rollers  58  are pretensioned into abutment on the corresponding second cams  14 . 
     When the camshaft  4  is rotated from the rotational position illustrated in  FIG. 1 , in which the base circles of the cams abut on the follower rollers  58  and  38 , the follower rollers  58  are downwardly urged (see position shown in  FIG. 5 ) in the counter-clockwise direction due to pivoting of the connecting lever  42 , wherein the eccentric device  32  rotates about the axis of the bushing  26  in a corresponding manner. The valve lever  6  is pivoted about the valve play-compensating element  8  by the first cam  12 , which abuts on the follower roller  38 , in accordance with the cam lobe of the first cam  12  for actuation of the valve  2 . 
     When the lobes of the second cam  14  have passed the follower rollers  58 , the follower rollers  58  return upwardly in the clockwise direction due to the pivoting of the connection lever  42 . The connecting lever  42  can advantageously pivot in the clockwise direction until its abutment surface  52  abuts on the stop  30 . In this position of the connecting lever  42 , the recess  50  aligns with the opening  28 , so that the piston  66  can extend due to the biasing by the hydraulic pressure and can enter into the recess  50 , whereby the connecting lever  42  is latched relative to the valve lever  6 . In the latched state, the valve lever  6  is actuated in accordance with the larger lobes of the second cams  14 , whereby the first cam  12  comes free from the follower roller  38 . 
     The locking of the connecting lever  42  can be released by reducing the hydraulic pressure acting on the piston  66  when the cam base circle is again passed over and the piston is pushed back into the valve lever  6  by the spring  70 . 
     The connecting lever  42  is advantageously provided with a bevel  76  ( FIG. 4 ) in the region of the abutment surface  52 ; the bevel  76  ensures that, when the connecting lever  42  pivots into abutment on the stop  30 , the piston  66 , which acts as a pin, is pushed back. 
       FIGS. 7 to 9  show the arrangement of  FIG. 1  in different perspective views and functional states.  FIG. 7  shows a position, in which the second cams are ineffective, i.e. the connecting lever is unlatched.  FIGS. 8 and 9  respectively show a null stroke position and a substantially full stroke position when the connecting lever is latched. 
     As is derivable from the preceding discussion, the inventive switchable valve actuating mechanism is very compactly constructed and includes slightly-moved inertial masses and a high stiffness. Further, the engagement of the cams takes place via the borne follower rollers  58  and  38 , which leads to low friction and thus fuel consumption advantages. 
     A sufficient energy storage capacity of the spring  54 , which provides for a secure abutment of the follower rollers  58  on the cams  14 , is important for the functional efficiency of the described valve actuating mechanism. In particular, at high rotational speeds, it must be ensured that the follower rollers  58  are always abutting the cams  14 . 
       FIG. 10  shows an embodiment, which is modified as compared to the described embodiment, in a side view similar to the view according to  FIG. 4 . 
     In the embodiment according to  FIG. 10 , two torsion springs  54   1  and  54   2  are inserted into two corresponding through-openings  48  (in FIG.  10 —not numbered) in place of the one torsion spring  54 ; the torsion springs  54   1  and  54   2  are supported on two protrusions  56   1  and  56   2  of the valve lever  6  and accordingly in two slots of opposing stops, which are formed on the connecting lever  42 . On the left in  FIG. 10 , the arrangement is illustrated with the follower roller abutting on the base circle of the cam  14 . On the right in  FIG. 10 , the arrangement is illustrated with the not-latched connecting lever and follower roller  58  maximally pivoted by the cam lobe of the cam  14  and the maximally-pivoted connecting lever  42 , respectively, wherein the cam  14  is ineffective for the actuation of the valve and in the illustrated example (null stroke), the inner cam  12  does not cause actuation of the valve. In this embodiment, which can switch between null stroke (no valve actuation) and valve actuation by the cams  14 , the follower roller  38  is not required to be provided. 
     In the embodiment according to  FIG. 11 , a curved helical spring  80  is utilized in place of the torsion spring(s); the helical spring  80  is supported between the protrusion  56  and/or stop formed on the valve lever  6  and another stop  82 , which is rigidly connected with the eccentric device  32  and thus is connected with the connecting lever  42  so as to rotate therewith. On the left in  FIG. 11 , the state of the helical spring  80  is illustrated when the follower roller  58  abuts on the cam base circle. On the right, the state is illustrated, in which the helical spring is maximally compressed, so that it holds the follower roller  58  in secure abutment on the cam  14  after the cam  14  has passed over the following roller  58 . 
     In the embodiment according to  FIG. 12 , a helical spring  80   1 , which operates in a bore of the valve lever  6 , is utilized in place of the curved helical spring  80  of  FIG. 11 ; the helical spring  80   1  is supported on a cam surface via a push rod  84 ; the push rod  84  is formed on a cam arm  86  that is connected so as to rotate with the eccentric device  32  and/or is rigidly connected with bearing pins  36  connected with the eccentric device  32 . The function of the arrangement according to  FIG. 12  otherwise corresponds to the function of  FIG. 11 . 
     In the embodiment according to  FIG. 13 , a tilting lever  88  borne on the valve lever  6  is utilized in place of the cam arm of  FIG. 12 ; one end of the tilting lever  88  follows the rotation of the eccentric device  32  and/or the movement of a bearing pin  36  rigidly connected with the eccentric device  32 ; a helical spring  80   2  is supported between the other end of the tilting lever  88  and the valve lever  6 . The function of the embodiment according to  FIG. 13  otherwise corresponds to the function of  FIG. 12 . 
     The above-described embodiments of return springs are only exemplary and can be modified in various ways and/or can be combined with each other. 
     The inventive valve actuating mechanism can be modified in various ways. The locking of the rotatability of the eccentric device can take place electromagnetically or in some other way. It is not required to provide three cams and three follower rollers. The illustrated embodiment provides, however, high symmetry and freedom from tilting forces that want to tilt the valve lever about its longitudinal axis. The adjustable engagement mechanism is not required to be disposed between the support, which is mounted on the engine housing, and the support on the valve of the lever. The components, which follow the cam contours, are not required to be rotatably borne, but rather can also be formed directly on the bushing and the bearing pin. The described rotatable bearing of the components located in direct abutment on the cams, as well as the rotatable bearing of the eccentric device inside of the valve lever, have the advantage, however, of very-low friction and high durability. The rotational direction of the eccentric device can be reversed relative to the illustrations. The connecting lever and the spring(s) can be disposed on the same or different sides of the valve lever, etc. 
     REFERENCE NUMBER LIST 
       2  Charge exchanging valve 
       4  Camshaft 
       6  Valve lever 
       8  Valve play-compensating element 
       12  Cam 
       14  Cain 
       16  Closing spring 
       18  End portion 
       20  End portion 
       22  Side part 
       24  Bushing-accommodation opening 
       26  Bushing 
       28  Opening 
       30  Stop 
       32  Eccentric device 
       34  Roller element 
       36  Bearing pin 
       38  Follower roller 
       40  Hole 
       42  Connecting lever 
       44  Slot 
       46  Projection 
       48  Through-opening 
       50  Recess 
       52  Abutment surface 
       54  Torsion spring 
       55  End leg 
       56  Protrusion 
       58  Follower roller 
       60  Washer 
       62  Cavity 
       64  Bore 
       66  Piston 
       68  Pin 
       70  Spring 
       72  Passage 
       74  Recess 
       76  Bevel 
       80  Helical spring 
       82  Stop 
       84  Push rod 
       86  Cam arm 
       88  Tilting lever