EP2396522B1 - Valve train of an internal combustion engine - Google Patents

Description

Field of the invention

The invention relates to a valve train of an internal combustion engine, comprising a carrier shaft and a rotatably mounted thereon and slidably disposed between two axial cam piece comprising at least one cam group immediately adjacent cams with different cam lobes and a Axialkulisse with two axially peripherally entgegenrekkenden on the circumference Has cam tracks, and with a coupled with the Axialkulisse actuator for moving the cam piece in the direction of both cam tracks.

Background of the invention

Such a valve train, which is used for variable actuation of gas exchange valves by means of sliding cam and in which a single actuator per cam piece is sufficient to move the cam piece in the direction of both cam tracks of Axialkulisse is considered from the considered generic DE 101 48 177 A1 previously known. There two cam pieces are disclosed with alternatively designed Axialkulissen, wherein the first Axialkulisse has a central guide bar to form inner guide walls for the actuator in the form of a dipping into the Axialkulisse cylindrical pin and the second Axialkulisse consists only of outer guide walls.

The latter embodiment has the advantage that the production cost for the axial slide is significantly smaller due to the omission of the guide bar. A considerable risk in terms of the reliability of the valve train in this embodiment, however, is that the displacement of the cam piece is completed completely, ie without a fault, if the mass inertia of the cam piece is sufficient to pass it through the crossing region of the curved paths without force of the cylinder pin to a certain extent in free flight to move to its other end position. A prerequisite for the sufficient inertia of the cam piece is of course a minimum speed of the camshaft, which directly from the friction between the cam piece and the Carrier shaft is dependent. A displacement of the cam piece rotating below this minimum rotational speed can cause the cam piece to stop "halfway" and a cam follower acting on the gas exchange valve to be acted upon by several cams of the cam group uncontrolled and under high mechanical loads simultaneously. In addition, there is no longer a way in this case to shift the cam piece by means of the cylindrical pin later in one of the end positions, since then the axial assignment between the cylinder pin and the outer guide walls is no longer given.

Although this function risk is significantly lower in the former embodiment of the Axialkulisse with central guide bar, the inner guide walls act at low speeds of the cam piece as the cylinder pin further accelerating forced operation. Nevertheless, there is also the risk here that the cylindrical pin does not engage in the predetermined curved path after passing through the crossing region, but also collides with the end face of the guide web under high mechanical load.

A valve train having the features of the preamble of claim 1 is also known from DE 101 48 178 A1 and the DE 10 2007 037 232 A1 out.

Object of the invention

The present invention is therefore the object of a valvetrain of the type mentioned in such a way that the said functional limitations and risks are at least partially eliminated. In concrete terms, the object is therefore, when using a single actuator for both Verschieberungen even at low speeds of the camshaft, for example during the starting process of the internal combustion engine, a successful, i. ensure complete switching of the cam piece.

Summary of the invention

The solution to this problem arises from the characterizing features of Claim 1, while advantageous developments and refinements of the invention are the dependent claims. Accordingly, the curved paths should be arranged one behind the other in the circumferential direction of the axial slide. A significant difference of the invention over the prior art thus relates to the mutual arrangement of the curved paths on the Axialkulisse, which now consecutively, ie in series, and no longer next to each other, ie in parallel, run and therefore no longer intersect. Due to the omission of the crossing region, the displacement of the cam piece takes place under permanent forced guidance of the axial slide against the actuating element coupled thereto, so that a complete switching operation of the cam piece is ensured even at the lowest rotational speeds of the camshaft.

With regard to the coupling of the actuating element with the Axialkulisse the cam tracks are each formed as a groove and the actuating element as engaging in the grooves cylindrical pin. Preferably, the curved paths are each of successive track sections composed with different axial strokes of the groove bounding groove walls, namely an entry section without Axialhub, a ramp section and a lifting section, wherein the lifting section has a significantly greater axial acceleration than the ramp section.

In addition, the cams should have a common base circle area, which begins at the latest with the ramp portion of the first curved path and ends at the earliest with the lifting portion of the second curved path. Since the common base circle region is to be understood as the angular range of the cam piece in which all the cams of the cam group are free of elevation, the displacement of the cam piece takes place only when the gas exchange valve associated with the cam group is closed and the cam to be engaged during the entire displacement operation also located in its base circle position. Thus, during the displacement process, no valve spring forces increasing the friction between the cam piece and the carrier shaft act on the cam piece. In order to keep the axial acceleration of the cam piece as small as possible, the beginning and the end of the base circle area and of the shifting process are ideally identical.

Further, the lifting sections may each be composed of successive Teilhubabschnitten with different radial strokes of the groove delimiting groove base, namely a first Teilhubabschnitt without radial stroke and a second Teilhubabschnitt with radially outwardly uplifting groove bottom. In contrast to the known in the prior art groove geometries in which the actuating pin is "ejected" only in axialkraftfreien state from the radially rising groove in its non-engaging rest position, it is expedient here to superimpose the Axialhub and the radial stroke of the groove to the each available cam angle of the lift sections to maximize and consequently to limit the comparatively high axial accelerations in the Hubabschnitten to a mechanically manageable level.

Finally, in the same background, it is provided that each of the second Teilhubabschnitt and the entrance section immediately adjacent to each other, wherein the groove bottom at the transition from the second Teilhubabschnitt to the entry section extends radially steeply sloping. In particular, with respect to the circumference of the Axialkulisse perpendicular sloping groove bottom, ie at a sum angle of the cam tracks of 360 °, thus, the cam angle of the lifting sections can be maximized for a given length of the intermediate section.

Brief description of the drawings

Figur 1

einen Ausschnitt eines erfindungsgemäßen Ventiltriebs im Längsschnitt;

Figur 2

die Axialkulisse in einer ersten perspektivischen Ansicht X gemäß Figur 5;

Figur 3

die Axialkulisse in einer zweiten perspektivischen Ansicht Y gemäß Figur 5;

Figur 4

die Axialkulisse in einer dritten perspektivischen Ansicht Z gemäß Figur 5;

Figur 5

eine Seitenansicht der Axialkulisse gemäß Figur 1 mit radialem Steuerdiagramm und

Figur 6

ein vollständiges Hubdiagramm der Axialkulisse.

Further features of the invention will become apparent from the following description and from the drawings, in which an embodiment of the invention is shown. Show it:

FIG. 1

a section of a valve gear according to the invention in longitudinal section;

FIG. 2

the axial backdrop in a first perspective view X according to FIG. 5 ;

FIG. 3

the axial backdrop in a second perspective view Y according to FIG. 5 ;

FIG. 4

the axial backdrop in a third perspective view Z according to FIG. 5 ;

FIG. 5

a side view of the axial slide according to FIG. 1 with radial control diagram and

FIG. 6

a complete lift diagram of the Axialkulisse.

Detailed description of the drawings

In FIG. 1 a section of a variable valve train of an internal combustion engine essential for the understanding of the invention is disclosed. The valve train points a camshaft 1, which a carrier shaft 2 and - the number of cylinders of the internal combustion engine accordingly - rotatably thereto and slidably disposed between two axial positions cam pieces 3 comprises. For the purpose of axial displacement, the carrier shaft 2 are provided with an outer longitudinal toothing and the cam piece 3 with a corresponding inner longitudinal toothing. The teeth are known per se and not shown here.

The cam piece 3 has on both sides of a bearing 4 arranged cam groups, each with two immediately adjacent cams 5 and 6, which have different cam elevations at the same base circle radius. The displacement of the cam piece takes place outside the cam elevations during the common base circle region of the cams 5, 6. The cam elevations are each in a known manner by a cam follower symbolized here only by a cam roller 7, e.g. a drag lever, selectively transmitted in dependence on the instantaneous axial position of the cam piece 3 to a gas exchange valve, not shown. The different cam elevations are to be understood as meaning different amounts of the respective cam lift and / or different valve control times of the cams 5, 6.

To switch between the cams 5 and 6, the cam piece 3 is provided with a manufactured as a single part and joined by means of interference fit Axialkulisse 8. On the circumference of the Axialkulisse 8 are two axially oppositely extending and circumferentially of the Axialkulisse 8 successively arranged cam tracks 9, 10 are formed in the form of grooves, in which an actuating element 11 can be coupled. This is closer from the FIGS. 2 to 4 in which the axial slide 8 is shown from different angle perspectives. The actuating element 11 is a cylindrical pin, which is part of a likewise known actuator, which is not explained here, for such valve trains. The cylinder pin 11 is axially fixed relative to the camshaft 1, but arranged radially displaceable in the internal combustion engine and serves to move the cam piece 3 in the direction of both cam tracks 9, 10th

The design of the curved paths 9, 10 results from a synopsis of FIGS. 2 to 6 , The in the FIGS. 2 to 4 shown views on the axial slide 8 correspond to the view arrows x, y and z in FIG. 5 in which the axial slide 8 shown in side view is additionally provided with a radial control diagram of the cam tracks 9, 10 according to the dashed line. The in the FIGS. 1, 2 and 5 Arrows indicated represent the direction of rotation of the camshaft 1. A complete lift diagram with radial and axial stroke of the cam tracks 9, 10 as a function of the camshaft angle goes out FIG. 6 out.

The two cam tracks 9, 10 each consist of successive track sections with different axial strokes (solid line in FIG FIG. 6 ) of the groove bounding groove walls 12 together. These track sections are an entry section F or C without axial stroke, a ramp section A or D for compensating axial position tolerances of the cylindrical pin 11 relative to the groove walls 12 and a lift section B or E, wherein the axial acceleration of the lift sections B, E is significantly greater than that of the ramp sections A, D. In the illustrated embodiment, the common base circle area of the cams 5, 6 is identical to the track sections A to E, ie the common base circle area begins with the ramp section A of the first cam track 9 and ends with the Lifting section E of the second curved path 10. In contrast, the cam elevations of the cams 5, 6 are in the region of the entry section F.

The lifting sections B and E are each composed of successive Teilhubabschnitten B1 and B2 or E1 and E2, which in the radial stroke of the groove bottom 13 (dashed line in FIGS. 5 and 6 ). In this case, the first Teilhubabschnitte B1 and E1 a groove bottom 13 with constant and identical to the sections F and A and C and D depth, while the groove base 13 rises radially outwardly over the second Teilhubabschnitte B2 and E2 to the cylinder pin 11 already eject during the sliding operation of the cam piece 3 from the respective groove in its non-engaging rest position. The switching of the cam piece 3 along the first cam track 9, ie from the currently active cam 5 on the cam 6 (see FIG. 1 ) takes place in that the dowel pin 11 is immersed in the insertion section F - depending on the size and duration of the cam elevation, this already takes place during the open gas exchange valve - and then the ramp section A and the stroke section B passes, while the rotating and the cylinder pin 11 supporting cam piece 3 is moved to its second axial position. Already in the course of the second Teilhubabschnitts B2 of the cylindrical pin 11 is lifted by the radially rising groove base 13 and ejected towards the end of the shifting process completely out of the curved path 9 in its non-engaging rest position.

Similarly, pushing back the cam piece 3 along the second curved path 10, i. from the then effective cam 6 on the cam 5 in that the dowel pin 11 dips into the insertion section C and then the ramp section D and the lift section E passes, while the rotating and the cylinder pin 11 supporting cam piece 3 is moved back to its first axial position , Here, too, the cylindrical pin 11 is raised in the course of the second Teilhubabschnitts E2 by the radially rising groove bottom 13 and ejected towards the end of the shifting process completely out of the curved path 10 in its non-engaging rest position.

Like from the FIGS. 2 to 5 becomes clear, in each case the second Teilhubabschnitt B2 or E2 and the entrance section C or F directly adjacent to each other, wherein the groove bottom 13 drops radially perpendicular to the transition of these sections, especially to maximize the length of the Hubabschnitts B for a given length of the Einfahrrabschnitts C. ,

In the FIG. 1 The locking device comprises two in a formed as a through hole radial bore 14 of the support shaft 2 diametrically opposed, slidably mounted locking body 15 and the inner circumference of the cam piece 3 extending, as circumferential grooves formed locking grooves 16 and 17, in which the force-loaded by a spring means 18 in radially outward direction locking body 15 are engaged in the respective associated axial positions.

When the locking bodies 15 are unilaterally open, thin-walled Blechumformteile. The open side is each as mounted in the radial bore 14 and formed as a helical compression spring spring means 18 enclosing hollow cylinder, while it is in the subsequent closed side each in the direction of the locking grooves 16, 17 tapered hollow body, the first conical and the front side is spherical. In order to ensure a low-resistance retraction of the locking body 15 in the radial bore 14 during the displacement operation of the cam piece 3, the locking body 15 are provided in the conical portion of the hollow body with a pressure relief opening 19.

The function of the locking device is not limited to the fixation of the cam piece 3 in the two axial positions, but also includes a braking of the cam piece 3 in its axial movement towards the end of Teilhubabschnitte B2 and E2. This braking is generated by contact friction of the spring-loaded locking body 15 on the both sides of the apex point 20 axially adjacent groove walls of the locking grooves 16, 17. Unlike in FIG. 1 illustrated, it is advantageous if the locking grooves 16, 17 are geometrically identical and the vertex 20 - based on the distance of the locking grooves 16, 17 associated axial positions of the cam piece 3 - runs centrally.

reference numerals

1

camshaft

2

carrier wave

3

cam piece

4

depository

5

cam

6

cam

7

cam roller

8th

axial slotted

9

first curved track

10

second curved track

11

Actuator / cylinder pin

12

groove wall

13

groove base

14

radial bore

15

latching body

16

locking groove

17

locking groove

18

Spring means / helical compression spring

19

Pressure relief opening

20

Vertex of Rastnuten

A

ramp section

B1,2

stroke section

C

entry section

D

ramp section

E1,2

stroke section

F

entry section

Claims (5)

1. Valve drive of an internal combustion engine, having a camshaft (1) which comprises a carrier shaft (2) and a cam piece (3) arranged rotationally conjointly on said carrier shaft so as to be displaceable between a first and a second axial position, which cam piece has at least one cam group of directly adjacent cams (5, 6) with different cam elevations and has an axial slotted guide (8) with a first and a second cam track (9, 10), which cam tracks are each in the form of a groove and extend on the circumference of the axial slotted guide (8) axially in opposite directions, and having an actuation element (11) which can be coupled to the axial slotted guide (8) and which is in the form of a cylindrical pin which engages into the grooves (9, 10) and which displaces the cam piece (3) from the first axial position into the second axial position along the first cam track (9) and from the second axial position into the first axial position along the second cam track (10), characterized in that the two cam tracks (9, 10) are arranged in series along the circumference of the axial slotted guide (8), and not adjacent to one another.
2. Valve drive according to Claim 1, characterised in that the cam tracks (9, 10) are each made up of successive track sections (F, A, B and C, D, E respectively) with different axial excursions of the groove walls (12) which delimit the groove, specifically a run-in section (F and C respectively) without axial excursion, a ramp section (A and D respectively) and an excursion section (B and E respectively), wherein the excursion section (B and E respectively) exhibits a considerably higher axial acceleration than the ramp section (A and D respectively).
3. Valve drive according to Claim 2, characterized in that the cams (5, 6) have a common base circle region which begins at the latest with the ramp section (A) of the first cam track (9) and ends at the earliest with the excursion section (E) of the second cam track (10).
4. Valve drive according to Claim 2, characterized in that the excursion sections (B, E) are each made up of successive partial excursion sections (B1, B2 and E1, E2 respectively) with different radial excursions of the groove base (13) which delimits the groove, specifically a first partial excursion section (B1 and E1 respectively) without radial excursion and a second partial excursion section (B2 and E2 respectively) with a groove base (13) that rises in a radially outward direction.
5. Valve drive according to Claim 4, characterized in that, in each case, the second partial excursion section (B2 and E2 respectively) and the run-in section (C and F respectively) directly adjoin one another, wherein, at the transition from the second partial excursion section (B2 and E2 respectively) to the run-in section (C and F respectively), the groove base (13) runs in a radially steeply falling manner and, in relation to the circumference of the axial slotted guide (8), preferably a perpendicularly falling manner.

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