Patent Publication Number: US-10781757-B2

Title: Variable valve drive of an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. Section 119 of German Patent Application No. DE 10 2018 118 099.3 filed Jul. 26, 2018, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to a variable valve drive of an internal combustion engine. 
     BACKGROUND 
     A variable valve drive is known from DE 10 2017 101 792 A1. This valve drive has a multiplicity of switchable rocker arms which are activatable by means of an elongated activation arm that is guided so as to be longitudinally displaceable on a cylinder head, wherein this activation arm has one connection element, which can be configured as a leaf spring, for each of the rocker arms to be activated. The axial displacement of the elongated activation arm is performed by a linear actuator that can be embodied as an electromagnet. By temporarily energizing and de-energizing the electromagnet, the tappet of the latter is axially retracted or deployed in order for the elongated activation arm to be displaced. 
     By virtue of the conjoint activation of the assigned rocker arms by means of the elongated activation arm and the leaf-spring-type connection elements fastened to the latter, in conjunction with a temporally rapid actuation, or an actuation at a comparatively high frequency of the electromagnet serving for displacing the elongated activation arm, undesirable oscillations and, associated therewith, erroneous switching of rocker arms can arise. This lies in that the linear actuator has a very short movement period of the armature of said linear actuator from an initial position to an axially maximum terminal position in which said armature axially displaces the elongated activation arm. This short movement period acts like an impulse, on account of which the elongated activation arm is intensely accelerated from the resting position of said activation arm. On account thereof, said activation arm loses contact with the tappet of the linear actuator, at the latest when said tappet returns to the terminal position. The elongated activation arm is subsequently decelerated by a resetting mechanism and is in an accelerated manner moved back to the tappet of the linear actuator until said activation arm impacts the tappet. Disadvantageous oscillations in the linear actuator, in the elongated activation arm, in the leaf springs, and in the switchable rocker arms are created in the motion sequence described, as is visualized in  FIG. 5 . 
     SUMMARY 
     The disclosure is therefore based on the object of proposing a valve drive having switchable rocker arms of the type mentioned at the outset, said valve drive by means of a linear actuator being adjustable in a oscillation-reduced manner. 
     This object is achieved by a variable valve drive which has the features described herein. 
     The disclosure thus proceeds from a variable valve drive of an internal combustion engine, having at least one gas exchange valve of identical function per cylinder, the valve stroke of said gas exchange valve predefined by cams of a camshaft and by means of at least one switchable rocker arm. The switchable rocker arm, having a first lever and a second lever, selectively transmits cam lift to the gas exchange valve. One end of one of the two levers is supported by an assigned support element that is mounted on a housing side. Another end of one of the two levers is supported on a valve stem of the gas exchange valve. The second lever is pivotably mounted to the first lever by means of a journal pin. The second lever, arranged with a roller to contact the cam, is selectively coupled to the first lever by means of a coupling. The coupling is activatable by means of an elongated activation arm on which one leaf spring is disposed for each coupling of one or more switchable rocker arms. The elongated activation arm, subjected to a resetting force of a resetting assembly, is longitudinally displaceable from a locking position to an unlocking position by means of a linear actuator. 
     In order for the object mentioned to be achieved, it is provided in the case of this valve drive that at least one damper mass is disposed or configured so as to be capable of oscillating on the elongated activation arm and/or on at least one leaf spring fastened to said elongated activation arm. 
     On account of this construction, undesirable oscillations within the valve drive, for example in the region of the linear actuator, of the elongated activation arm, of the leaf springs, as well as the switchable rocker arms are at least reduced and at best completely neutralized. Moreover, the noise generation of the valve drive is reduced. A space-saving synchronous activation of the coupling elements of the individual switchable rocker arms by way of only one central linear actuator is possible on account of the leaf springs which are disposed on the elongated activation arm and can be configured to be contoured. The natural frequency of the damper mass that is disposed in a oscillation-capable manner is chosen in such a manner that the harmful oscillation energy on account of said damper mass is neutralized by the resonant frequency of the valve drive and/or is converted to oscillation-related thermal energy. 
     According to one embodiment, it is provided that the at least one damper mass is disposed or configured on the end side on a pendulum arm which by way of the damper-mass-free end thereof is articulated so as to be freely pivotable on the elongated activation arm. Consequently, a construction which can make do without any additional spring elements is provided. 
     In the case of one other embodiment, it is provided that the at least one damper mass is formed by at least one ball, wherein said ball is disposed on the elongated activation arm so as to be displaceable in an axially sprung manner between two mutually opposite damper springs. On account thereof, a three-dimensionally space-saving integration of the damper mass in the elongated activation arm is achieved. 
     According to one further embodiment, it can be provided that the at least one damper mass is formed by at least one integral thickening on at least one leaf spring. Consequently, a configuration of the necessary damper mass is implementable without any additional constructive components. 
     The at least one thickening can be formed by folding over at least once a material portion of at least one leaf spring. On account thereof, the at least one damper mass can be configured integrally on the elongated activation arm by means of known forming methods such as, for example, edge-bending, folding, rabbeting, or the like. 
     The at least one thickening can be linked in a sprung manner to the leaf spring by means of a single-ply material web of said leaf spring. Consequently, a damper mass that has been integrally shaped by means of thickening can at the same time be linked in a sprung manner to the elongated activation arm in order for a spring-mass system to be achieved. 
     It is furthermore provided that the linear actuator can be configured as an electromagnet having an armature that is guided so as to be axially movable in a coil, wherein the armature at an axial end is rigidly connected to a tappet. A reliable axial displacement of the elongated activation arm is ensured on account of the electromagnet. The fluid lines, which are otherwise required for activating the coupling elements with the aid of pneumatic or hydraulic cylinders and which in spatial terms are difficult to integrate in a cylinder head of the internal combustion engine, can be dispensed with. An electric line having two poles and a comparatively small line cross section is sufficient for energizing the electromagnet. 
     Moreover, it can advantageously be provided that the elongated activation arm at one axial end thereof has an angled contact tab on which the tappet of the linear actuator can engage for activating the elongated activation arm. Consequently, the tappet can act on the elongated activation arm only so as to push but not actively pull so that the transmission of vibrations between the mentioned components of the valve drive is reduced, said oscillations under certain circumstances potentially leading to material failure and increased noise emissions. 
     In terms of the switchable rocker arms it can furthermore be provided that the respective coupling of the switchable rocker arms has a locking bolt which is displaceable so as to be parallel to the first lever and has a guide pin which is received in a diagonally running groove-type gate-type guide of an activation bolt, wherein the activation bolt is oriented so as to be transverse to the locking bolt and by means of the spring element is pretensioned in an axially outward manner in the direction of the leaf spring assigned to the respective coupling. On account thereof, a spatially particularly compact construction of the couplings of the switchable rocker arms is provided. 
     Each locking bolt can have a protrusion which in the locking position of the switchable rocker arm engages below at least portions of the bearing face of the second lever. On account thereof, a reliable locking of the two levers of the switchable rocker arm that acts on one side is provided. 
     The elongated activation arm can be guided in guide elements so as to be axially displaceable on a cylinder head of the internal combustion engine. Consequently, a space-saving disposal of the elongated activation arm on the cylinder head of the internal combustion engine is guaranteed. The elongated activation arm as well as the leaf springs, configured so as to be contoured, for example, have a comparatively high mechanical rigidity and can be embodied in a simple as well as cost-effective manner as stamped components from a steel sheet or from a light-metal sheet. Alternatively thereto, the leaf springs can also be produced as separate sheet-metal formed parts and be connected in a permanent and vibration-resistant manner to the elongated activation arm by means of suitable fastening elements such as, for example, rivets, bolts or screws. 
     In order for any migration or kinking of the elongated activation arm under an operative load to be avoided, the activation arm can be guided so as to be axially displaceable in a multiplicity of axially uniformly mutually spaced apart guide openings on the cylinder head of the internal combustion engine. At least some of said guide openings for the elongated activation arm for reasons of simplified ease of production can be integrated in the bearing caps of an assigned camshaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order for the disclosure to be more readily understood, a drawing in which exemplary embodiments are illustrated is appended to the description. In the drawings: 
         FIG. 1  shows a schematic lateral view of a switchable rocker arm of a valve drive in a locking position thereof; 
         FIG. 2  shows a partially sectional rear view of the rocker arm according to  FIG. 1 , together with an assigned leaf spring which is fastened to an elongated activation arm; 
         FIG. 3  shows an expanded illustration of the valve drive according to  FIG. 1 , having two rocker arms in the locking position thereof, said rocker arms being activatable by means of a linear actuator and the elongated activation arm; 
         FIG. 4  shows the valve drive according to  FIG. 3 , having the two rocker arms in an unlocking position thereof; 
         FIG. 5  shows a diagram with a temporal profile of the actuation path of a tappet of the linear actuator of the valve drive according to  FIGS. 3 and 4 ; 
         FIG. 6  shows a schematic perspective view of the elongated activation arm according to  FIG. 2 , having a first embodiment of a damper mass; 
         FIG. 7  shows a schematic perspective view of the elongated activation arm according to  FIG. 2 , having a second embodiment of a damper mass; and 
         FIG. 8  shows a perspective view of a leaf spring of the activation arm according to  FIG. 2 , having a third embodiment of a damper mass. 
     
    
    
     DETAILED DESCRIPTION 
     Accordingly,  FIG. 1  shows a schematic lateral view of a switchable rocker arm  12  of a variable valve drive  10 . The valve drive  10  is part of a reciprocating piston internal combustion engine (not illustrated in more detail) and serves for activating inlet or outlet valves of the internal combustion engine. The switchable rocker arm  12  has a frame-shaped first lever  14  and a second lever  16  that is disposed so as to be mounted pivotably in said first lever  14 . Moreover, the rocker arm possesses a coupling  20  by means of which the two levers  14 ,  16  are capable of being fixedly coupled together such that the second lever  16  can no longer swing in relation to the first lever  14 . The coupling  20  in  FIG. 1  is situated in the locking position thereof. In the unlocking position (not illustrated here) the first lever  14  and the second lever  16  by means of the coupling  20  are mechanically decoupled from one another such that the second lever  16  can pivot in relation to the first lever  14 . 
     A first end  28  of the frame-shaped first lever  14  is supported by means of a support element  30  which is received on the cylinder head  26  and has an integrated hydraulic valve lash compensation element. The first lever  14  at the second end  32  thereof that faces away from said support element  30  is supported by way of a journal pin  24  on a valve stem  34  of a gas exchange valve  36  of the internal combustion engine. A roller  38  which is in contact with a cam  40  of a rotatable camshaft  42  of the internal combustion engine and which for minimizing the friction of the valve drive  10  is fastened so as to be rotatably mounted on the second lever  16 . The two levers  14 ,  16  by means of the spring force of a contact pressure spring  22  which is configured as a leg spring are mutually braced in such a manner that the second lever  16  is constantly pressed against the assigned cam  40 . 
     In the locking position illustrated in  FIG. 1 , a latch-type protrusion  48  of a locking bolt  50  of the coupling  20  engages below a lower-side bearing face  52  of the second lever  16  such that the second lever  16  is reliably locked in an oscillation-resistant manner to the first lever  14 . In the locking position of the switchable rocker arm  12 , the typical activation of the gas exchange valve  36  is performed by the rotating cam  40  which is in contact with the roller  38  of the second lever  16  and periodically presses down the roller  38 , on account of which the first lever  14  which, by means of the coupling  20 , is locked to the second lever  16  and is likewise conjointly moved and activates the gas exchange valve  36 . 
     In order for the rocker arm  12 , proceeding from the locking position shown in  FIG. 1 , to be switched to the unlocking position it is necessary for the locking bolt  50  to be axially displaceable in the first lever  14  to be displaced axially so far in the direction of the first end  28  of the first lever  14  that the latch-type protrusion  48  no longer engages below the bearing face  52  of the second lever  16  but releases the bearing face  52 . For this purpose, the locking bolt  50  includes a guide pin  56  (possibly cylindrical in shape) arranged in a lower side, which is received in a diagonally running, groove-type gate-type guide  58  of an activation bolt  60  of the first lever  14 , said activation bolt  60  being oriented and displaceable transversely to the locking bolt  50 , that is to say, perpendicularly to the image plane. The displacement of the activation bolt  60  which is performed perpendicularly to the image plane is performed by means of an elongated activation arm  84 , illustrated for example in  FIG. 2 , which here is configured as a flexurally rigid thrust strip, for example, to which orthogonally disposed leaf springs  82  are fastened (see  FIGS. 2 to 4 , as well as  FIGS. 6 to 8 ). 
     The first lever  14  and the second lever  16 , in terms of the pivotability of the second lever  16 , are mechanically decoupled from one another in the unlocking position such that the rotating cam  40  on the camshaft  42 , counter to the force effect of the contact pressure spring  22 , does indeed periodically press down and, in turn, move the second lever  16  by means of the roller  38 , but the second lever  16  can no longer utilize the latch-type protrusion  48  of the retracted locking bolt  50  as a support element. On account thereof, the actuation or activation, respectively, of the gas exchange valve  36  is suppressed. Accordingly, the second lever  16  in the unlocking position as before does indeed periodically deflect in the case of a rotating camshaft  42 , but does not entrain the first lever  14  in this pivoting movement. 
       FIG. 2  shows a partially sectional rear side view of the rocker arm  12  according to  FIG. 1  at the side of the support element, together with the mentioned elongated activation arm  84 . The rocker arm  12  of the valve drive  10  is supported in the region of the first end  28  of the first lever  14 , as can be seen. A valve spring retainer  66  of the valve stem  34  (not to be seen in this view) of the gas exchange valve  36  is disposed in the region of the second end  32  of the first lever  14 , said second end  32  facing away from the support element  30 . As has already been explained, the activation of the second lever  16  by way of the roller  38  rotatably disposed there is performed by means of the cam  40  of the camshaft  42 . The coupling  20  can be particularly readily seen in the sectional illustration of  FIG. 2 . 
     The coupling  20  has the locking bolt  50  which in this illustration is oriented so as to be substantially perpendicular to the image plane and which has the guide pin  56  which is disposed so as to be orthogonal to the locking bolt  50  and which is received so as to be displaceable in the gate-type guide  58  of the activation bolt  60 . The activation bolt  60  is received in a cylindrical bore  68  of the first lever  14  so as to be longitudinally displaceable between a first end-side detent  70  and a second end-side detent  72 . A spring element  76  which here is configured as a cylindrical compression spring is supported on the first detent  70  and on the first end portion  74  of the activation bolt  60 . 
     A tapered activation pin  80  which at the end side is rounded in a convex manner is configured on a second end portion  78  of the activation bolt  60 , said second end portion  78  facing away from the first end portion  74  of the activation bolt  60 , said activation pin  80  by virtue of the force effect of the axially pretensioned spring element  76  bearing in an axially sprung manner on a leaf spring  82  of an elongated activation arm  84  that is configured as a thrust strip, said leaf spring  82  here configured in only an exemplary manner so as to be contoured in a bent manner. 
     The leaf spring  82  is disposed so as to be substantially orthogonal to the elongated activation arm  84 . By virtue of the force effect of the spring element  76  on the rocker arm side, the activation bolt  60 , upon sliding into the bore  68  by means of the leaf spring  82  of the elongated activation arm  84 , returns in a self-acting manner to the non-activated resting position of said activation bolt  60  shown here, in which the rocker arm is in the locking position. On account of the axial sliding of the activation bolt  60 , counter to the force effect of the spring element  76 , into the bore  68  by an axial actuation path s, the rocker arm  12  proceeding from the locking position of the coupling  20  illustrated in  FIG. 2  can be moved to the unlocking position of said coupling  20 . On account of displacement movement of the elongated activation arm  84  performed counter to the actuation path s, the coupling  20  is switched back to the locking position thereof (see  FIGS. 3 and 4 ). The activation of the activation bolt  60  is performed by way of the leaf spring  82  that is fastened to the elongated activation arm  84 . This applies to all of the switchable rocker arms  12 ,  12   a  that are present within the valve drive  10 . 
       FIGS. 3 and 4 , to which reference is made at the same time in the further course of the description, in  FIG. 3  show an expanded illustration of the valve drive  10  according to  FIG. 1 , having two rocker arms  12 ,  12   a  which are disposed in a directly neighboring manner and which by means of a linear actuator  90  are activatable by way of the elongated activation arm  84 . The couplings  20  of the switchable rocker arms  12 ,  12   a  in  FIG. 3  are in the static locking position thereof, while  FIG. 4  shows the valve drive  10  in a situation in which the couplings  20  of the rocker arms  12 ,  12   a  are situated just before reaching the unlocking position thereof. 
     The two gas exchange valves  36  are activatable by means of the two rocker arms  12 ,  12   a  as well as the camshaft  42  having in each case the assigned cams  40  of the valve drive  10  of the internal combustion engine. Each of the two switchable rocker arms  12 ,  12   a  of the valve drive  10  shown here only in an exemplary manner possesses an activation bolt  60  which is in each case activatable by means of an assigned contoured leaf spring  82  of the elongated activation arm  84 . The elongated activation arm  84  by means of guides (not illustrated) is guided so as to be longitudinally displaceable on the cylinder head  26  of the internal combustion engine and by means of the linear actuator  90  is displaceable by the axial actuation path s. 
     The linear actuator  90  in this exemplary embodiment is configured as an electromagnet  92  which has a substantially hollow cylindrical coil  94  in which an axially movable armature  96  is received. The armature  96  at one axial end  98  has a substantially cylindrical tappet  100 . The elongated activation arm  84 , at an axial end thereof that faces the linear actuator  90  for coupling to the tappet  100 , has an angled contact tab  102  on which the tappet  100  can engage in order for the elongated activation arm  84  to be activated. In the non-energized state, or the voltage-free state, respectively, of the electromagnet  92  the tappet  100  by means of an actuator-internal spring (not illustrated) retracts axially in a self-acting manner to the position shown in  FIG. 3 . 
     The elongated activation arm  84  accordingly serves for the synchronous activation of the activation bolt  60  of the two rocker arms  12 ,  12   a.  Said elongated activation arm  84  can be produced in a simple and cost-effective manner as a standard component from a steel sheet or from a light-metal sheet. The contoured leaf springs  82  as well as the contact tab  102  can be molded integrally on the elongated activation arm  84  and/or as separate components be riveted, screwed, adhesively bonded, or otherwise fastened to said elongated activation arm  84 . 
     In the situation illustrated in  FIG. 3  the linear actuator  90 , or the electromagnet  92 , respectively, is illustrated so as to be non-energized and the tappet  100  so as to be axially retracted such that the contoured leaf springs  82  are at least slightly lifted from the activation bolt  60  of the rocker arms  12 ,  12   a  and the couplings  20  of the rocker arms  12 ,  12   a  are therefore situated in the locking position thereof. A switch from the locking position to the unlocking position of the couplings  20  of the rocker arms  12 ,  12   a  in the case of a non-energized linear actuator  90  is performed by axially sliding the elongated activation arm  84  backward, counter to the actuation path s in  FIG. 3 , with the aid of a spring-loaded resetting assembly  104  which exerts an axial resetting force FR on the activation arm  84 . 
     As opposed to  FIG. 3 , the electromagnet  92  in  FIG. 4  is illustrated so as to be energized such that the tappet  100  has assumed the maximum axial deployment position thereof. Consequently, the leaf springs  82  of the elongated activation arm  84  press the activation bolt  60  of the two rocker arms  12 ,  12   a  practically completely into the assigned bores  68  such that the couplings  20  of the two rocker arms  12  are switched synchronously to the unlocking position of said couplings  20 . 
     It is also relevant in this context that the tappet  100 , and conjointly therewith the elongated activation arm  84 , are very intensely accelerated on account of the impulse-like energizing of the electromagnet  92 . The tappet, loaded by an actuator-internal restoring spring, subsequently returns to the non-activated position of said tappet. Consequently, the contact tab  102  of the elongated activation arm  84  is lifted from the tappet  100 , and the activation arm  84  moves on its own until the actuation bolt  60  on the actuator side impacts the mentioned detent  72  on the rocker arm side. After the coupling  20  has been switched to the unlocking position thereof, the elongated activation arm  84 , driven by the spring effect of the respective leaf springs  82  and the axial resetting force FR, moves back toward the tappet  100  of the linear actuator  90 , the contact tab  102  of the elongated activation arm  84  finally impacting the free end of said tappet  100 . 
     By virtue of the movements described, in particular of the tappet  100  and of the contact tab  102  of the elongated activation arm  84 , undesirable mechanical oscillations or vibrations, respectively, can arise within the valve drive  10 . This effect is moreover facilitated on account of the high actuation frequencies of up to  100  Hz of the linear actuator  90  of the valve drive  10  which are required in the operation of an internal combustion engine. Said undesirable oscillations can be effectively eliminated or else at least largely eliminated with the aid of the present disclosure. 
       FIG. 5  shows a diagram  110  in which the time tin seconds is plotted on the independent axis of said diagram  110 . The actuation path a of the tappet  100  of the linear actuator  90  is plotted in millimeters on the dependent axis of the diagram  110  on the left side, and the electrical control voltage U in Volts of a switching signal that is applied to the electromagnet is plotted on the dependent axis on the right side. The diagram  110  moreover shows a temporal profile  112  of the control voltage U which serves for periodically energizing the linear actuator  90  of the valve drive  10 , said actuator  90  being configured as an electromagnet. Moreover, a temporal profile  114  of an actuation path a of the tappet  100  of the linear actuator  90  of the valve drive  10  according to  FIGS. 3 and 4  is illustrated. 
     The axial actuation path s of the elongated activation arm  84  having the leaf springs  82 , as well as the actuation paths of the individual activation bolt  60  of the switchable rocker arms  12 ,  12   a,  at least in the case of a purely static observation, are substantially congruent with the temporal profile  114  of the axial actuation path a of the tappet  100  of the linear actuator  90  visualized here (path a≈path s). 
     The control voltage U applied to the linear actuator  90 , or to the electromagnet  92  thereof, respectively, has an approximately rectangular temporal profile  112  having a period duration At of approximately  0 . 15  seconds. With an ascending flank  116  of the profile  112  of the control voltage U the switching of the rocker arms  12 ,  12   a  commences from the respective locking position to the unlocking position, while the switching back of the rocker arms  12 ,  12   a  from the unlocking position to the locking position is conversely initiated with a descending flank  118  in the profile  112  of the control voltage U. 
     As can be seen in the diagram  110 , significant mechanical oscillations  120 ,  122  arise on the tappet  100  and thus also at least partially on the elongated activation arm  84  having the leaf springs  82 , primarily in the region of the ascending flank  116  and of the descending flank  118  in the temporal profile  114  of the actuation path a of the tappet  100 . The same applies in an analogous manner to the axial activation paths of the activation bolt  60  of the switchable rocker arms  12 ,  12   a.    
     The oscillations  120 ,  122  have an approximately sinusoidal amplitude which exponentially decreases with the time t. The declared objective of the present disclosure is to ideally completely dampen these oscillations  120 ,  122  that are introduced into the elongated activation arm  84 , or into the linear actuator  90 , respectively, so as to avoid erroneous controlling of the switchable rocker arms  12  of the valve drive  10  in particular in the case of comparatively high actuation frequencies of the linear actuator  90 , and to reduce the noise generation on the linear actuator  90 . To this end, a damper mass which is connected to the elongated activation arm  84  so as to be capable of oscillating is utilized. The disclosure will therefore be illustrated in detail herein. 
       FIG. 6  schematically shows a perspective view of the elongated activation arm  84  according to  FIG. 2  having a first embodiment of a damper mass. The elongated activation arm  84 , configured as a thrust strip or a thrust bar, presently possesses in only an exemplary manner six contoured leaf springs  82  that are disposed so as to be approximately orthogonal, in order for a corresponding number of switchable rocker arms  12 ,  12   a  (not illustrated in the drawing here) of the valve drive  10  to be activated. The elongated activation arm  84  in the case of a non-energized or inactive, respectively, linear actuator  90 , by means of the resetting assembly  104  is pushed back by the mechanical force FR in the direction toward the linear actuator  90  such that the switchable rocker arms  12 ,  12   a,  proceeding from the unlocking position of the couplings  20 , switch back to the respective locking positions. This resetting process is moreover facilitated by the axially decompressing leaf springs  82 . 
     As can be seen, a solid damper mass  130  is disposed on an end side of a pendulum arm  132 , between two axially directly neighboring leaf springs  82  of the elongated activation arm  84 . An end  134  of the pendulum arm  132  that is distant from the damper mass herein is articulated so as to be freely pivotable in a fulcrum  136  of a tab  138  of the elongated activation arm  84 . The tab  138  is integrally molded so as to be orthogonal on the elongated activation arm  84 , or as a separate component is fastened to the latter. 
     A pivot axis (not illustrated) which on the tab  138  of the articulated pendulum arm  132  runs so as to be perpendicular to the image plane, runs so as to be spaced apart in a substantially parallel manner to a longitudinal side  140  of the activation arm  84  that faces the leaf springs  82 , said activation arm  84  here in an exemplary manner having a substantially rectangular cross-sectional geometry. The damper mass  130  has a three-dimensional shape which substantially corresponds to that of a sectoral fragment of a hollow cylinder. The damper mass  130  that is articulated so as to be pivotable on the elongated activation arm  84 , when interacting with the pendulum arm  132 , acts as a mass-spring system. 
     The elongated activation arm  84  is actuated at up to  100  Hz by means of the linear actuator  90  (not illustrated here) which engages on the contact tab  102 , and consequently is periodically displaced back and forth in a reciprocal manner at this frequency by the axial actuation path s. The damper mass  130  that is articulated so as to swing on the elongated activation arm  84  is in turn thus excited so as to perform oscillating movements which are symbolized by a small double arrow  142 . The mass of the damper mass  130 , for achieving an optimal oscillation damping effect, is dimensioned such that said mass ideally completely compensates the oscillations of the elongated activation arm  84 , having the leaf springs  82  disposed thereon, to be eliminated. 
       FIG. 7  schematically shows a perspective view of the elongated activation arm according to  FIG. 2  having a second embodiment of a damper mass according to the disclosure. Deviating from the first embodiment illustrated in  FIG. 6 , a rectangular recess  150  in which a damper mass  160  is disposed is formed here between two directly neighboring leaf springs  82  in the elongated activation arm  84 . The actuation of the elongated activation arm  84  having the leaf springs  82  disposed thereon is performed by means of the tappet  100  of the linear actuator  90  (not illustrated here), by way of the angled contact tab  102  of the activation arm  84 . By virtue of said actuation, the elongated activation arm  84  is axially displaceable by the actuation path s. 
     An approximately cuboid first protrusion  152  and a second protrusion  154  are molded so as to be mutually opposite in the region of a narrow side of the rectangular recess  150 , said narrow side not being identified for the sake of improved clarity in the drawing. The two protrusions  152 ,  154  are configured so as to be mutually aligned while leaving an intermediate space  156 , and so as to be flush with a narrow side  158  of the elongated activation arm  84  that has a rectangular cross-section geometry. A damper mass  160  is received in an axially sprung manner in the intermediate space  156 , between mutually facing free ends of a first and a second damper spring  164 ,  166 , wherein the two damper springs  164 ,  166  are in each case configured as cylindrical compression springs and in portions are in each case received on one of the protrusions  152 ,  154 . The damper springs  164 ,  166  are in each case supported on the narrow sides of the rectangular recess  150 . 
     The damper mass  160  here in only an exemplary manner is configured as a solid ball  162 ; alternatively thereto, said damper mass  160  can also have a geometry that deviates therefrom. For example, the damper mass  160  can be configured as a solid cylinder having in each case tapered ends which are capable of being received in the free ends of the damper springs  164 ,  166 . Alternatively thereto, a continuous cylindrical damper spring (not illustrated in the drawing) can be clamped on both sides axially between the two protrusions  152 ,  154 , wherein the spherical or a cylindrical damper mass can be fastened for example by press-fitting, jamming, adhesive bonding, or in another manner, so as to be centric within the damper spring which in terms of the diameter thereof is correspondingly dimensioned. 
     The mass of the ball  162  which by means of the damper springs  164 ,  166  is mounted so as to be axially sprung, in combination with the spring forces of the two damper springs  164 ,  166 , for achieving optimal results is again dimensioned such that the natural frequency of said ball  162  in terms of oscillation damping corresponds to a frequency of the valve drive  10  that is primarily to be dampened, and in particular of the elongated activation arm  84  having the contoured leaf springs  82  disposed thereon. 
       FIG. 8  shows a perspective view of a leaf spring  82  of the elongated activation arm  84  according to  FIG. 2  having a third embodiment of a damper mass. The contoured leaf spring  82  of the valve drive  10  possesses a fastening portion  170  having a cylindrical bore (not identified). An angled portion  172  which is edge-bent by approximately 90° adjoins the fastening portion  170 , said angled portion  172  in turn transitioning to a first rectilinear portion  174 , a slightly contoured intermediate portion  176 , or an intermediate portion  176  that runs so as to be slightly inclined, respectively, as well as a second rectilinear portion  178 , the latter acting as a contact face, or activation face, respectively, for the activation bolt  60  of the switchable rocker arms  12 ,  12   a.  The angled portion  172  has an approximately quadrant-shaped geometry. The two rectilinear portions  174 ,  178  that are separated by the intermediate portion  176  run so as to be substantially mutually parallel. 
     Two mutually opposite thickenings  184 ,  186  which in each case act as a compact or massive, respectively, damper mass  180 ,  182  on both sides of the rectilinear portion  174  here are in each case molded integrally from a material portion  188  of the leaf spring  82 . The thickenings  184 ,  186  on both sides can be implemented, for example, by folding a part of an assigned material portion  188  of the leaf spring  82  multiple times in a meandering manner. The two damper masses  180 ,  182  are moreover in each case linked to the first rectilinear portion  174  by means of a single-ply material web  190 ,  192  which lies in a plane of the first rectilinear portion  174 . The single-ply material webs  190 ,  192  act like elastic damper springs for linking the two compact damper masses  180 ,  182  to the leaf springs  82  in a spring-elastic manner. 
     Moreover, a natural frequency of the damper masses  180 ,  182  that are connected in a sprung manner to the leaf spring  82  is adapted to an undesirable primary oscillation of the valve drive  10  to be ideally completely eliminated, or of the elongated activation arm  84  (not plotted here) and/or of the leaf springs  82  of the latter, respectively. 
     The material webs  190 ,  192  having the compact damper masses  180 ,  182  configured thereon at the end sides likewise run so as to be parallel to a plane that is defined by the second rectilinear portion  178 , wherein the second rectilinear portion  178  in turn is specified as a contact face for an activation bolt  60  of the switchable rocker arms  12 ,  12   a  of the valve drive  10 . 
     The integral configuration of the two damper masses  180 ,  182 , and the linkage thereof by means of the single-ply material webs  190 ,  192  that act like damper springs is readily implementable using conventional sheet-metal forming methods. Forming methods of this type permit a cost-effective production of the leaf springs  82  and/or of the elongated activation arm  84  that is suitable for large volumes, along with a high dimensional accuracy that is reliably reproducible. 
     LIST OF REFERENCE CHARACTERS 
     
         
           10  Variable valve drive 
           12  Switchable rocker arm 
           12   a  Switchable rocker arm 
           14  First lever of the rocker arm 
           16  Second lever of the rocker arm 
           20  Coupling of the rocker arm 
           22  Contact pressure spring, leg spring of the rocker arm 
           24  Journal pin of the rocker arm 
           26  Cylinder head of an internal combustion engine 
           28  First end of the rocker arm 
           30  Support element, hydraulic valve lash compensation element 
           32  Second end of the rocker arm 
           34  Valve stem of a gas exchange valve 
           36  Gas exchange valve 
           38  Roller on the second lever of the rocker arm 
           40  Cams of a camshaft 
           42  Camshaft 
           48  Latch-type protrusion on the locking bolt 
           50  Locking bolt 
           52  Bearing face on the second lever of the rocker arm 
           54  Arrow, activation direction 
           56  Guide pin 
           58  Gate-type guide 
           60  Activation bolt 
           66  Valve spring retainer 
           68  Bore 
           70  First detent 
           72  Second detent 
           74  First end portion of the activation bolt 
           76  Spring element for the activation bolt 
           78  Second end portion of the activation bolt 
           80  Activation pin 
           82  Contoured leaf spring 
           84  Elongated activation arm 
           90  Linear actuator 
           92  Electromagnet of the linear actuator 
           94  Coil of the electromagnet 
           96  Armature of the linear actuator 
           98  Axial end of the armature 
           100  Tappet 
           102  Angled contact tab of the activation arm 
           104  Resetting assembly for the elongated activation arm 
           110  Diagram 
           112  Profile of a control voltage U 
           114  Profile of the actuation path a of the tappet 
           116  Ascending flank of the control voltage U 
           118  Descending flank of the control voltage U 
           120  First oscillation 
           122  Second oscillation 
           130  Damper mass 
           132  Pendulum arm 
           134  Damper-mass-free end of the pendulum arm 
           136  Fulcrum 
           138  Tab 
           140  Longitudinal side of the activation arm 
           142  Double arrow, oscillation movement 
           150  Rectangular recess 
           152  First protrusion in the recess 
           154  Second protrusion in the recess 
           156  Intermediate space 
           158  Narrow side of the activation arm 
           160  Damper mass 
           162  Ball 
           164  First damper spring 
           166  Second damper spring 
           170  Fastening portion 
           172  Angle portion 
           174  First rectilinear portion 
           176  Contoured intermediate portion 
           178  Second rectilinear portion 
           180  Damper mass 
           182  Damper mass 
           184  First thickening 
           186  Second thickening 
           188  Material portion of the leaf spring 
           190  First single-ply material web 
           192  Second single-ply material web 
         a Axial actuation path of the tappet of the linear actuator 
         FR Resetting force of the resetting assembly 
         s Axial actuation path of the elongated activation arm 
         t Time 
         U Control voltage