Switchable valve actuating mechanism

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.

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 claim1is 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.

DETAILED DESCRIPTION OF THE INVENTION

A charge exchanging valve2, for example an intake valve of an internal combustion engine, according to the Figures is actuated by a camshaft4with a valve lever6disposed therebetween. One end of the valve lever6is supported on a known hydraulic valve play-compensating element8and the other end is supported on the shaft of the valve2; the valve lever6abuts on cams12and14, respectively, between the ends of the valve lever6in a manner that will be further discussed below. As is apparent, a middle first cam12is formed with a smaller lobe than second, side cams14, which accommodate the first cam12therebetween. A valve closing spring is denoted with16. The hydraulic valve play-compensating element8acts so that the valve lever6is in play-free abutment on at least one of the cams and on the shaft of the valve, respectively.

FIG. 2shows the valve lever6and the components mounted thereon in exploded perspective illustration.

The valve lever6includes two end portions18and20, which are connected to each other via spaced-apart side parts22. A bushing-accommodation opening24penetrates through the side parts22; a bushing26is insertable in the opening24.

The end portion18, which abuts on the valve play-compensating element8, has a hollow interior and includes a side opening28.

As shown inFIG. 2, a stop30is formed on the lower, left side of the end portion18. An eccentric device32is insertable into the bushing26; cylindrical roller elements34are disposed along the eccentric device32so that the eccentric device32is rotatable in the bushing26.

Bearing pins36project from the side surfaces of the eccentric device32eccentrically to the rotational axis of the eccentric device32, which rotational axis is coaxial to the axis of the bushing26in the assembled state; the bearing pins36are coaxially aligned.

A follower ring and/or a follower roller38is insertable in a slot37formed between the side parts22of the valve lever6; the inner side of the follower roller38is provided with not-illustrated roller elements; the follower roller38is borne by these roller elements in a state slidable on the bushing26.

A hole40of a connecting lever42is slidable onto the left bearing pin36according toFIG. 2; the connecting lever42includes a lateral projection46(FIG. 6) formed with a slot44, which projection46fits in a through-opening48of the eccentric device32. One end portion of the connecting lever42includes a recess50and an abutment surface52.

A torsion spring54is insertable into the through-opening48; one end leg (not illustrated) of the torsion spring54can engage in the slot44of the connecting lever and the other end leg55of the torsion spring54can be supported on a protrusion56of the valve lever6(cf.FIGS. 4,8and9).

Follower rings and/or follower rollers58can be borne on the bearing pins36via roller elements provided in the follower rollers58. The follower rollers58are advantageously disposed on the bearing pins36between washers60, wherein the outer washers60are advantageously formed as locking rings that axially secure the follower rollers58on the bearing pins36.

The end portion18of the valve lever6includes a cylindrical cavity62that ends in the opening28at the left according toFIG. 3and merges in a bore64to the right.

A piston66, which has a U-shaped cross-section as a whole, is inserted in the cavity62; the piston66is held by a pin68that penetrates through the piston body and is screwed into the bore64. A spring70is supported between the pin68and the piston66. A portion of the cavity62, which is located to the right of the piston body inFIG. 3, is connected with a recess74via a passage72; the valve lever6abuts on the valve play-compensating element8via the recess74. The passage72and thus the piston66are biased with hydraulic pressure from the valve play-compensating element8.

The components illustrated inFIG. 2are assembled, for example, as follows:

The follower roller38is introduced into the slot37of the valve lever6. The bushing26is then inserted, so that the bushing is held in the opening24and the follower roller38is rotatably borne on the bushing26. The eccentric device32is inserted into the bushing26, so that the eccentric device32is rotatable as a whole about the axis of the bushing26. The torsion spring54is inserted into the through-opening48of the eccentric device32. Then, the connecting lever42and one follower roller58are pushed from one side onto one bearing pin36and the other follower roller58is pushed onto the other bearing pin36, wherein washers are disposed in between if desired. The follower rollers58are secured on the bearing pins36by lock washers.

The piston66is inserted into the opening28and is secured by the pin68; the spring70is disposed therebetween.

The resulting assembly is disposed on the valve play-compensating element and the shaft of the valve2. The legs of the torsion spring54are mounted such that the connecting lever42and the eccentric device32, which is connected with the connecting lever42so as to rotate therewith, respectively, are pretensioned for one rotation in the clockwise direction, i.e. the follower rollers58are pretensioned into abutment on the corresponding second cams14.

When the camshaft4is rotated from the rotational position illustrated inFIG. 1, in which the base circles of the cams abut on the follower rollers58and38, the follower rollers58are downwardly urged (see position shown inFIG. 5) in the counter-clockwise direction due to pivoting of the connecting lever42, wherein the eccentric device32rotates about the axis of the bushing26in a corresponding manner. The valve lever6is pivoted about the valve play-compensating element8by the first cam12, which abuts on the follower roller38, in accordance with the cam lobe of the first cam12for actuation of the valve2.

When the lobes of the second cam14have passed the follower rollers58, the follower rollers58return upwardly in the clockwise direction due to the pivoting of the connection lever42. The connecting lever42can advantageously pivot in the clockwise direction until its abutment surface52abuts on the stop30. In this position of the connecting lever42, the recess50aligns with the opening28, so that the piston66can extend due to the biasing by the hydraulic pressure and can enter into the recess50, whereby the connecting lever42is latched relative to the valve lever6. In the latched state, the valve lever6is actuated in accordance with the larger lobes of the second cams14, whereby the first cam12comes free from the follower roller38.

The locking of the connecting lever42can be released by reducing the hydraulic pressure acting on the piston66when the cam base circle is again passed over and the piston is pushed back into the valve lever6by the spring70.

The connecting lever42is advantageously provided with a bevel76(FIG. 4) in the region of the abutment surface52; the bevel76ensures that, when the connecting lever42pivots into abutment on the stop30, the piston66, which acts as a pin, is pushed back.

FIGS. 7 to 9show the arrangement ofFIG. 1in different perspective views and functional states.FIG. 7shows a position, in which the second cams are ineffective, i.e. the connecting lever is unlatched.FIGS. 8 and 9respectively 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 rollers58and38, which leads to low friction and thus fuel consumption advantages.

A sufficient energy storage capacity of the spring54, which provides for a secure abutment of the follower rollers58on the cams14, 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 rollers58are always abutting the cams14.

FIG. 10shows an embodiment, which is modified as compared to the described embodiment, in a side view similar to the view according toFIG. 4.

In the embodiment according toFIG. 10, two torsion springs541and542are inserted into two corresponding through-openings48(in FIG.10—not numbered) in place of the one torsion spring54; the torsion springs541and542are supported on two protrusions561and562of the valve lever6and accordingly in two slots of opposing stops, which are formed on the connecting lever42. On the left inFIG. 10, the arrangement is illustrated with the follower roller abutting on the base circle of the cam14. On the right inFIG. 10, the arrangement is illustrated with the not-latched connecting lever and follower roller58maximally pivoted by the cam lobe of the cam14and the maximally-pivoted connecting lever42, respectively, wherein the cam14is ineffective for the actuation of the valve and in the illustrated example (null stroke), the inner cam12does not cause actuation of the valve. In this embodiment, which can switch between null stroke (no valve actuation) and valve actuation by the cams14, the follower roller38is not required to be provided.

In the embodiment according toFIG. 11, a curved helical spring80is utilized in place of the torsion spring(s); the helical spring80is supported between the protrusion56and/or stop formed on the valve lever6and another stop82, which is rigidly connected with the eccentric device32and thus is connected with the connecting lever42so as to rotate therewith. On the left inFIG. 11, the state of the helical spring80is illustrated when the follower roller58abuts 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 roller58in secure abutment on the cam14after the cam14has passed over the following roller58.

In the embodiment according toFIG. 12, a helical spring801, which operates in a bore of the valve lever6, is utilized in place of the curved helical spring80ofFIG. 11; the helical spring801is supported on a cam surface via a push rod84; the push rod84is formed on a cam arm86that is connected so as to rotate with the eccentric device32and/or is rigidly connected with bearing pins36connected with the eccentric device32. The function of the arrangement according toFIG. 12otherwise corresponds to the function ofFIG. 11.

In the embodiment according toFIG. 13, a tilting lever88borne on the valve lever6is utilized in place of the cam arm ofFIG. 12; one end of the tilting lever88follows the rotation of the eccentric device32and/or the movement of a bearing pin36rigidly connected with the eccentric device32; a helical spring802is supported between the other end of the tilting lever88and the valve lever6. The function of the embodiment according toFIG. 13otherwise corresponds to the function ofFIG. 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.

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