Patent Application
20200032718
This disclosure relates to a variable valve drive of an internal combustion engine.
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
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.
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:
Accordingly,
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
In order for the rocker arm 12, proceeding from the locking position shown in
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.
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
The two gas exchange valves 36 are activatable by means of the two rocker arms 12, 12a 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, 12a 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
The elongated activation arm 84 accordingly serves for the synchronous activation of the activation bolt 60 of the two rocker arms 12, 12a. 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
As opposed to
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.
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, 12a, 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, 12a commences from the respective locking position to the unlocking position, while the switching back of the rocker arms 12, 12a 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, 12a.
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.
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.
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.
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, 12a 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 118 099.3 | Jul 2018 | DE | national |
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.
