VARIABLE VALVE DRIVE HAVING A ROCKER LEVER

Abstract

The present disclosure relates to a variable valve drive for a lifting valve, in particular for a charge-exchange valve of an internal combustion engine, which is periodically movable between a closed position and an open position indirectly by way of a cam via a rocker lever. The variable valve drive includes a switchable rocker lever arrangement for the actuation of the lifting valve, having a transmission rocker lever and a valve rocker lever which are mounted pivotably on different rocker lever axles which are each parallel to the camshaft axis.

Claims

1. A variable valve drive for a lifting valve, in particular for a charge-exchange valve of an internal combustion engine, which is periodically movable between a closed position and an open position indirectly by way of a cam of a camshaft, comprising: a switchable rocker lever arrangement for the actuation of the lifting valve, having a transmission rocker lever and a valve rocker lever which are mounted so as to be pivotable on different rocker lever axles which are each parallel to a camshaft axis, wherein the valve rocker lever, at a first end, is in operative contact with the lifting valve and, at a second end, has a roller, wherein the transmission rocker lever, at a first end, is in engagement with a cam of a camshaft and, at a second end, is operatively connected, by way of a contour surface, to the roller of the valve rocker lever, in such a way that a rocking movement of the transmission rocker lever generates a rocking movement of the valve rocker lever, during which the roller of the valve rocker lever rolls on the contour surface; and an actuating device for the switching of the rocker lever arrangement, by way of which actuating device the contour surface can be rotated about the rocker lever axle of the transmission rocker lever by means of a planetary gearing, in order to generate a displacement of a rolling region of the roller of the valve rocker lever on the contour surface.

2. The variable valve drive according to claim 1, wherein the transmission rocker lever includes: at least one planet gear of the planetary gearing, which at least one planet gear is guided by a planet carrier element of the transmission rocker lever, wherein the planet carrier element has the first end which engages with a cam of the camshaft, and an internal gear of the planetary gearing, which internal gear has the contour surface on the outer circumference and engages into the at least one planet gear; and further comprising a sun gear of the planetary gearing connected rotationally conjointly to a shaft which can be rotated by the actuating device.

3. The variable valve drive according to claim 2, wherein the actuating device comprises an electrical, electromechanical, mechanical or hydraulic actuating unit, by means of which, for the adjustment of the valve lift, a rotational position of the shaft bearing the sun gear is adjustable.

4. The variable valve drive according to claim 1, wherein the contour surface has a first rolling region which forms in particular a base circle contour which generates no valve lift when the roller of the valve rocker lever rolls on the base circle contour, and has a second rolling region which adjoins the first rolling region and which has a ramp contour.

5. The variable valve drive according to claim 4, wherein the contour surface has a third rolling region which adjoins the second rolling region and which generates a valve position with maximum valve lift when the roller of the valve rocker lever rolls on the third rolling region.

6. The variable valve drive the shaft bearing the sun gear according to claim 2, wherein the actuating device is designed to vary a rotational position of the shaft bearing the sun gear in a continuously variable fashion.

7. The variable valve drive the shaft bearing the sun gear according to claim 2, wherein the actuating device is designed to vary a rotational position of the shaft bearing the sun gear into two predetermined positions, such that switching is possible between two different valve lifts.

8. The variable valve drive according to claim 1, wherein the transmission rocker lever is preloaded by way of a restoring spring such that the transmission rocker lever is pushed against the camshaft.

9. The variable valve drive according to claim 5, wherein the contour surface has a fourth rolling region, which adjoins the third rolling region and which forms a ramp contour, and a fifth rolling region, which adjoins the fourth rolling region, wherein the fifth rolling region has a constant radial spacing to the axis of the rocker lever axle of the transmission lever, which spacing is greater than the radial spacing of the third rolling region and greater than the radial spacing of the first rolling region.

10. An arrangement comprising: at least two variable valve drives, each variable valve drive including, a switchable rocker lever arrangement for the actuation of the lifting valve, having a transmission rocker lever and a valve rocker lever which are mounted so as to be pivotable on different rocker lever axles which are each parallel to a camshaft axis, wherein the valve rocker lever, at a first end, is in operative contact with the lifting valve and, at a second end, has a roller, wherein the transmission rocker lever, at a first end, is in engagement with a cam of a camshaft and, at a second end, is operatively connected, by way of a contour surface, to the roller of the valve rocker lever, in such a way that a rocking movement of the transmission rocker lever generates a rocking movement of the valve rocker lever, during which the roller of the valve rocker lever rolls on the contour surface; and an actuating device for the switching of the rocker lever arrangement, by way of which actuating device the contour surface can be rotated about the rocker lever axle of the transmission rocker lever by means of a planetary gearing, in order to generate a displacement of a rolling region of the roller of the valve rocker lever on the contour surface, wherein the transmission rocker levers each have a common first rocker lever axis, the valve rocker levers each have a common second rocker lever axis, and the at least two variable valve drives have a common actuating device in the form of an electric motor, wherein the electric motor is operatively connected to a shaft which is coaxial with respect to the first rocker lever axis.

11. A motor vehicle, in particular utility vehicle, having a having a variable valve drive comprising: a switchable rocker lever arrangement for the actuation of the lifting valve, having a transmission rocker lever and a valve rocker lever which are mounted so as to be pivotable on different rocker lever axles which are each parallel to a camshaft axis, wherein the valve rocker lever, at a first end, is in operative contact with the lifting valve and, at a second end, has a roller, wherein the transmission rocker lever, at a first end, is in engagement with a cam of a camshaft and, at a second end, is operatively connected, by way of a contour surface, to the roller of the valve rocker lever, in such a way that a rocking movement of the transmission rocker lever generates a rocking movement of the valve rocker lever, during which the roller of the valve rocker lever rolls on the contour surface; and an actuating device for the switching of the rocker lever arrangement, by way of which actuating device the contour surface can be rotated about the rocker lever axle of the transmission rocker lever by means of a planetary gearing, in order to generate a displacement of a rolling region of the roller of the valve rocker lever on the contour surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above-described embodiments and features of the present disclosure may be combined with one another as desired. Further details and advantages of the present disclosure will be described below with reference to the appended drawings, in which:

[0034] FIG. 1 shows a side view of a valve drive according to an embodiment of the present disclosure;

[0035] FIG. 2 shows a perspective exploded illustration of a transmission rocker lever according to an embodiment of the present disclosure;

[0036] FIG. 3 shows a perspective illustration of a valve drive according to an embodiment of the present disclosure;

[0037] FIG. 4 shows a detail view of the coupling between valve rocker lever and transmission rocker lever according to an embodiment of the present disclosure;

[0038] FIG. 5 shows a side view of an internal gear (toothing not shown) with the contour surface according to a further embodiment of the present disclosure; and

[0039] FIG. 6 shows an illustration of various settable lift curves of the lifting valve.

[0040] Identical parts are denoted by the same reference designations in the figures, such that the various views of the valve drive shown in the figures can be understood from this also.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a side view of a variable valve drive 1 according to an embodiment of the present disclosure. FIG. 3 shows a corresponding perspective view. The valve drive 1 serves for the actuation of charge exchange valves (not shown) of an internal combustion engine, which charge exchange valves are periodically movable between a closed position and an open position indirectly by way of a cam 2 of a camshaft 3.

[0042] The valve drive 1 includes a switchable rocker lever arrangement for the actuation of the lifting valves. The rocker lever arrangement includes a first rocker lever (valve rocker lever) 20, which is mounted so as to be pivotable about a rocker lever axle 23, and a second rocker lever (transmission rocker lever) 10, which is mounted so as to be pivotable about a further rocker lever axle 13. The two rocker lever axles 13, 23 are spatially separate but are both parallel to the axis 3a of the camshaft 3.

[0043] The valve rocker lever 20 is, at a valve-side end 21, that is to say by way of its valve-side lever arm 21, in operative contact with two lifting valves (not shown). The valve-side lever arm 21 of the valve rocker lever 20 is, for this purpose, designed as a two-valve lever arm for the purposes of actuating two charge exchange valves simultaneously. For this purpose, the valve-side lever arm 21 is of forked form, as can be seen in FIG. 3. As can also be seen in FIG. 3, two such valve rocker lever arrangements are arranged one behind the other in an axial direction of the camshaft for the purposes of actuating four lifting valves. This arrangement of the two valve drives is denoted in its entirety by the reference 100.

[0044] A receptacle 24 is arranged at each valve-side end of the lever arm 21. The receptacle 24 may be used for the mounting of a hydraulic valve-clearance compensating element 25 such as is known per se. Instead of a hydraulic valve-clearance compensating element, it is also possible, with corresponding machining, for there to be received in the receptacle 24 a screw with an elephant-foot configuration, by way of which a valve clearance can be manually readjusted.

[0045] Hydraulic valve-clearance compensating elements in internal combustion engines are known per se and serve for compensating in particular the changes in length dimensions of the charge exchange valves over the service life, in such a way that reliable valve closure is ensured in the base circle phase of the cam that actuates the valve. Here, it is on the other hand sought for the cam lift to be transmitted to the valve, and thus converted into a valve lifting movement, without losses. The mode of operation of such hydraulic valve-clearance compensating elements which are arranged in the force flow of a valve controller, in particular of an internal combustion engine, is assumed to be known.

[0046] The valve rocker lever 20 is held on a rocker lever bearing block (not shown), wherein the rocker lever axle 23 is arranged on the rocker lever bearing block, onto which rocker lever axle the valve rocker lever 20 is, by way of an associated bore, pivotably mounted and held by way of an axial position-securing means. In the present exemplary embodiment, the axial position-securing means is designed as an engagement element-counterpart element connection between the bearing block and the rocker lever, in the case of which an engagement element oriented transversely with respect to the axial direction, for example in the form of a ring-shaped web 27, engages pivotably into an associated counterpart element (not illustrated) with axial flank support. The axial position-securing means may however also be realized, in a manner known per se, by way of abutment surfaces on the rocker lever flanks. Said flanks may be created for example by calibration of the forged blank or by mechanical machining. At the bearing block side, the fixing may likewise be realized by way of correspondingly machined surfaces and by way of discs and securing rings. Furthermore, axial position-securing means between a rocker lever and the axle are known. For example, for this purpose, a region of the axle which is surrounded by the bore of the rocker lever has a ring-shaped groove in which there runs a circlip, which simultaneously runs by way of its outer ring-shaped section in a ring-shaped groove of the rocker lever.

[0047] At its opposite end 22 in relation to the rocker axle 23, that is to say at the camshaft-side lever arm 22, a roller 26 is arranged on the distal end of the lever arm 22.

[0048] The transmission rocker lever 10 is in engagement, at a camshaft-side end 11, with the cam 2 of the camshaft 3. For this purpose, a roller 18, for example a thrust roller, is arranged on the camshaft-side end 11, which roller rolls on the cam 2 of the camshaft 3 and thus picks off the cam movement. The transmission rocker lever 10 is furthermore, at the other end 12 in relation to the rocker lever axle 13, operatively connected by way of a lift-defining surface, referred to as contour surface 16, to the roller 26 of the valve rocker lever 20, that is to say the roller 26 of the valve rocker lever 20 rolls on the contour surface 16 during a rocking movement of the transmission rocker lever 10 generated by the cam movement, whereby a corresponding rocking movement of the valve rocker lever 20 is generated. The transmission rocker lever 10, by way of its rocking movement, transmits the cam movement to the valve rocker lever 20, which in turn, by way of its correspondingly resulting rocking movement, generates the valve lift. In this way, the transmission rocker lever 10 and valve rocker lever 20 are connected in series. The camshaft 3 and valve rocker lever 20 may, for this purpose, be designed in a manner known per se, and are coupled to one another in terms of movement by way of the transmission lever 10 arranged in between.

[0049] The contour surface 16 on which the valve rocker lever roller 26 is supported serves as a rolling region on which the valve rocker lever roller 26 rolls back and forth during the transmission of the rocking movement of the transmission rocker lever 10 to the valve rocker lever 20. The lift characteristic of the lifting valve can thus be predefined, and also varied, by way of the design of said contour surface 16 which serves as rolling surface.

[0050] As can be seen in FIG. 1, the cam movement is transmitted via a planetary gearing 19. Here, the transmission rocker lever 10 has a planet carrier element 14 which, at its camshaft-side end 11, has the mounted roller 18. At its opposite end, the planet carrier element 14 guides three planet carriers 17, which are arranged in an internal gear 15 which is pressed into the planet carrier element and which mesh with the internal teeth 15a thereof. The planet carriers 17 furthermore mesh with a sun gear (not visible) which is arranged on the shaft 13 and which is thus positioned at the central point of the planet carrier arrangement.

[0051] The cam contour is thus picked off by the planet carrier element 14, whose angular magnitude of the tilting movement remains constant independently of a set valve lift throughout operation. The tilting of the planet carrier element 14 and the resulting rotation of the planet gears 17 result in the rotation of the internal gear 15 with a corresponding transmission ratio. The internal gear 15 is part of a component, also referred to in this case as second lever of the transmission rocker lever, which forms the lift-predefining contour surface 16 on which the rocker lever roller 26 of the rocker lever 20 rolls. As a result of the tilting of the planet carrier element 14, the internal gear 15 with the roller contour 16 rotates with a corresponding transmission ratio. Here, the rocker lever roller 26 rolls on the roller contour 16 and accordingly opens the valves.

[0052] The sun gear is arranged rotationally conjointly on a continuously extending shaft 30 which is designed to extend continuously across all cylinders and which thus has a respective sun gear for each cylinder. The continuously extending shaft is connected to an electric motor (not shown) as electric motor, which with corresponding actuation can rotate the continuously extending shaft 30 in targeted fashion for the purposes of adjusting the valve lift and/or the valve opening times and valve closing times.

[0053] An advantage of the present disclosure thus lies in the simultaneous control of the variability of the valve lift across all cylinders by means of only one actuating motor, which performs only a rotational movement with a small rotational angle magnitude.

[0054] The cam follower lever 15 is preloaded by way of a restoring spring 17 via a restoring spring abutment point 17a, such that the entire transmission rocker lever 10 is forced against the camshaft 3 by the spring force of the restoring spring.

[0055] The above-described construction of the transmission rocker lever 10 can be clearly seen in the perspective exploded illustration of FIG. 2. The planet carrier element 14 guides planet gears 17 which are guided in each case by means of a pin between a receiving element 14a and a cover 14c of the planet carrier element 14, wherein the cover 14c is fastened by way of three countersunk screws 14d to the three support elements 14b.

[0056] FIG. 4 shows a detail view of the coupling between valve rocker lever 20 and the transmission rocker lever 10 at the contour surface 16. In this exemplary embodiment, the contour surface 16 has three different regions 16a, 16b and 16c, which can serve as rolling regions for the roller 26.

[0057] The first rolling region 16a forms the base circle contour, that is to say the valve rocker lever 20 generates no valve lift when the roller 26 rolls on said region. The spacing of the points on the first rolling surface 16a to the axis of the rocker lever axle 13, that is to say the radial spacing R1 thereof, is constant. The contour surface 16 furthermore includes a second rolling region 16b which directly adjoins the first rolling region 16a and which has a ramp contour. On the second rolling region, the radial spacing of the rolling points increases from a value R1 to a value R2. Thus, if the roller 26 rolls on the second region 16b proceeding from the first region 16a, the valve rocker lever 20 rocks more the further the roller 26 rolls on the second rolling region 16b. Consequently, the valve lift that is generated is greater the further the roller 26 of the valve rocker lever 20 rolls on the second rolling region 16b proceeding from the first rolling region 16a.

[0058] The second rolling region 16b is adjoined by a third rolling region 16c, which has a constant radial spacing R2 and which generates a valve position with maximum valve lift if the roller 26 of the valve rocker lever 20 rolls on the third rolling region 16c.

[0059] As already described above, the valve drive 1 includes an electric motor as an actuating device for varying the rotational position of the sun gear shaft 30. Through variation of the rational position of the sun gear shaft 30, the contour surface 16 is likewise rotated about the rocker lever axle 13 of the transmission rocker lever 10 in order to generate a displacement of a rolling region of the roller 26 of the valve rocker lever 20 on the contour surface 16. In this way, that region of the contour surface 16 which is rolled on, that is to say picked off, by the roller of the valve rocker lever is varied, along with the resulting valve lift and/or the valve opening and/or closing times.

[0060] By means of the targeted variation of the rotational position of the sun gear shaft 30, it is thus possible for the rotational position of that component of the transmission rocker lever which includes the ring gear 15 relative to the planet carrier element 14 to be varied in order to vary a rolling region of the roller 26 of the valve rocker lever 20 on the contour surface 16. In each of the different settable rotational positions, planet carrier element and internal gear 15 are then again coupled in terms of movement with regard to a pivoting movement (rocking movement) about the rocker lever axle 13.

[0061] For example, the actuating device may be designed to set two different rotational positions of the internal gear 15 or of the contour surface 16 relative to the planet carrier element 14, resulting in two different rolling regions for the roller 26 of the valve rocker lever 10. For this usage situation, it would also be possible to utilize a conventional hydraulic camshaft adjuster instead of an electric motor.

[0062] In a first set rotational position, during a rocking movement of the transmission rocker lever 10 generated by the cam 2, it is possible, purely by way of example, for the roller 26 to roll back and forth on a first rolling region, which encompasses almost the entire first rolling region 16a and a first subregion of the second rolling region 16b. By contrast, in a second set rotational position, during a rocking movement of the transmission rocker lever 10 or of the internal gear 15 generated by the cam 2, it is possible for the roller 26 to roll back and forth on the second rolling region, which encompasses almost the entire second rolling region 16b and a subregion of the third rolling region 16c.

[0063] If the valve drive 1 is switched from the first rolling region to the second rolling region, the valve lift that can be generated by the camshaft 3 is increased.

[0064] The actuating device may be designed such that it can set a rotational position of the second lever relative to the first lever into two predetermined positions, such that switching is possible between two different, predetermined rolling regions on the contour surface 16, and thus valve lifts. Alternatively, the actuating device may also be designed such that more than two predetermined rotational positions can be set, or the rotational position is continuously variable within predefined limits. In the latter variant, the valve lift can be varied in continuous fashion.

[0065] FIG. 5 shows a side view of the internal gear 15 with the contour surface 516 of the transmission rocker lever 10 according to a further embodiment of the present disclosure. In this embodiment, the contour surface 516 has five different rolling regions 16a-16e. The first rolling region 16a again forms the base circle contour with constant radial spacing R1 to the axis of the axle 13. The adjoining second rolling region 16b in turn forms a ramp contour with an increasing radial spacing, which radial spacing has increased to the value R2 at the end of the second rolling region. The adjoining third rolling region 16c then in turn forms a region with a constant radial spacing R2.

[0066] Said third rolling region 16c is then adjoined, in the rolling direction, by a fourth rolling region 16d, which in turn forms a ramp contour. At the end of the fourth rolling region 16d, the radial spacing has increased to the value R3. The fourth region is then adjoined by a fifth rolling region 16e, which in turn has a constant radial spacing. The rolling points on the fifth rolling region 16e have a constant radial spacing to the axis of the rocker lever axle of the transmission lever. The radial spacing R3 of the fifth rolling region 16e is greater than the radial spacing R2 of the third rolling region 16c and greater than the radial spacing R1 of the first rolling region 16a. In this design variant with five rolling regions, the third region 16c forms a middle position, in which the lifting valve is briefly, that is to say when the roller 26 rolls on the third region 16c, held open in an open position with a constant lift height which is smaller than the maximum lift height.

[0067] FIG. 6 illustrates different lift curves that can be set by way of the valve drive. The angle of rotation a of the camshaft 3 is plotted on the abscissa. The valve lift d is plotted on the ordinate. The curves 61 to 64 show four different settable valve lift profiles as a function of the angle of rotation of the camshaft. Each of the four curves 61 to 64 corresponds to a particular rotational position, set by way of the actuating device, of the second lever 15 relative to the first lever 14 of the transmission rocker lever 10. Here, the curve 61 corresponds to a set rotational position which generates the largest valve lift and the shortest valve closing times, whereas, by contrast, the curve 65 generates the smallest valve lift and the longest valve closing times. In the variant 61, therefore, a roof-shaped lift curve can be realized by virtue of the valves being briefly held open at a constant valve lift. Through symmetrical reduction in size or enlargement of the lift curve, it is thus likewise possible for the opening and closing times of the valves to be varied.

[0068] Even though the present disclosure has been described with reference to particular exemplary embodiments, it is self-evident to a person skilled in the art that numerous changes may be made, and equivalents used as substitutes, without departing from the scope of the present disclosure. Furthermore, numerous modifications may be made without departing from the associated scope. Consequently, the present disclosure is not intended to be restricted to the exemplary embodiments disclosed, but rather is intended to encompass all exemplary embodiments which fall within the scope of the appended patent claims. In particular, the present disclosure also claims protection for the subject matter and the features of the subclaims independently of the claims to which reference is made.

LIST OF REFERENCE DESIGNATIONS

[0069] 1 Variable valve drive [0070] 2 Cam [0071] 3 Camshaft [0072] 3a Camshaft axis [0073] 10 Transmission rocker lever [0074] 11 First end [0075] 12 Second end [0076] 13 Rocker lever axle of the transmission rocker lever [0077] 14 Planet carrier element [0078] 14a Receiving element [0079] 14b Support element [0080] 14c Cover [0081] 14d Countersunk screw [0082] 14e Pin [0083] 15 Internal gear [0084] 15a Internal teeth [0085] 16, 516 Contour surface [0086] 16a, 16b, 16c, 16d, 16e Rolling regions [0087] 17 Planet gear [0088] 18 Roller [0089] 19 Planetary gearing [0090] 20 Valve rocker lever [0091] 21 First end or valve-side lever arm [0092] 22 Second end or camshaft-side lever arm [0093] 23 Rocker lever axle of the valve rocker lever [0094] 24 Receptacle [0095] 25 Hydraulic valve-clearance compensating element [0096] 26 Roller [0097] 27 Ring-shaped web [0098] 30 Sun gear shaft [0099] 31 Restoring spring [0100] 61-65 Valve lift profile curve [0101] 100 Arrangement [0102] R1, R2, R3 Radial spacing