DE102012218803A1 - Valve gear of an internal combustion engine - Google Patents

Abstract

A sliding cam valve train of an internal combustion engine is proposed. A cam piece (3) that can be displaced on a support shaft (2) between two axial positions comprises a group of cams (4, 5) immediately adjacent, a groove-shaped axial link (8) and a locking device (10, 11, 12) which define the axial positions of the cam piece the carrier wave stabilized. According to the invention, the control times of the axial link and the gas exchange valve (7) should always overlap, so that at least one of the cam lobes opens the gas exchange valve at a camshaft angle (αV0) that is still within the axial stroke phase of the shifting cam piece.

Description

• – eine Nockenwelle mit einer Trägerwelle und einem Nockenstück, das auf der Trägerwelle drehfest und zwischen zumindest zwei Axialpositionen verschiebbar angeordnet ist und das eine Nockengruppe unmittelbar benachbarter Nocken mit voneinander verschiedenen Erhebungen und eine nutförmige Axialkulisse aufweist, sowie mit einer Rastiervorrichtung, die die Axialpositionen des Nockenstücks auf der Trägerwelle stabilisiert;
• – einen Aktuator mit einem in die Axialkulisse einkoppelbaren Betätigungsstift zum Verschieben des Nockenstücks;
• – und einen Nockenfolger, der die Erhebungen selektiv abgreift und auf ein Gaswechselventil überträgt.

The invention relates to a valve train of an internal combustion engine, comprising:

• - A camshaft having a support shaft and a cam piece which is rotatably mounted on the support shaft and slidably disposed between at least two axial positions and having a cam group of immediately adjacent cams with mutually different elevations and a groove-shaped Axialkulisse, and with a Rastiervorrichtung, the axial positions of the cam piece stabilized on the carrier shaft;
• - An actuator with an engageable in the Axialkulisse actuating pin for moving the cam piece;
• - And a cam follower, which selectively picks up the surveys and transmits to a gas exchange valve.

Background of the invention

Such a valve train is for example from the DE 10 2004 008 670 A1 known. To displace the cam piece engages the relatively axially stationary actuating pin in the rotating axial groove whose axial stroke forces the cam piece to move on the carrier shaft. The displacement of the cam piece between two axial positions must take place within the angular range of the camshaft in which all cam lobes are lift-free, ie in time within the common base circle phase of all lobes. Otherwise, the cam follower, typically the cam roller of a finger lever, would be actuated simultaneously by two cams of the still far displaced cam piece during the following elevation phase and, in the worst case, tilt the finger lever down from its pivot bearing.

Due to the extensive component tolerance chain in the valve train the engagement of the actuating pin in the axial groove is always subject to axial play, so that the displacement of the cam piece results not only from the mutual positive guidance of actuating pin and axial groove, but also from inertial free flight phases of the cam piece relative to the actuating pin. The inertia of the sliding cam piece is used to a particular extent in axial scenes with intersecting slide tracks, which only have an accelerating groove flank before their crossing point and only a retarding groove flank after the intersection point. The DE 101 48 177 A1 shows such Axialkulisse, wherein a successful displacement operation of the cam piece its sufficient mass inertia and consequently - with additional consideration of the friction - requires a sufficiently high dynamics corresponding to a minimum speed of the camshaft.

As previously explained, the axial stroke of the axial slide, i. their kinematics are such that the cam piece is moved in a timely manner and sufficiently far between the axial positions in the largest possible speed range. Decisively decisive for the kinematic design of the Axialkulisse are acting on the cam piece acceleration, inertia and friction forces and the sum of the component tolerances. Conversely, the kinematics of the Axial Kulisse has a direct influence on the contact forces between the actuating pin and the groove flanks, said contact forces even at high axial accelerations of the cam piece, i. must remain bearable at high camshaft speeds or a short base circle phase of the cam lobes.

Object of the invention

The present invention has the object, a valvetrain of the type mentioned in such a way that the kinematics of the Axialkulisse even at high camshaft speeds and / or short base circle phases leads to moderate contact forces between the actuating pin and the groove flanks of the Axialkulisse.

Summary of the invention

The solution to this problem results from the fact that the dynamic displacement of the cam piece from the first to the second axial position always has the following relationship: h _S (α _V = α _V0 ) <h _R

α_V

= Drehwinkel der Nockenwelle;

α_V0

= Drehwinkel der Nockenwelle, bei dem der Nockenfolger beginnt, das Gaswechselventil mit der in der zweiten Axialposition übertragenen Erhebung zu öffnen;

h_S

= momentaner Verschiebeweg des Nockenstücks bezüglich der ersten Axialposition;

h_R

= axialer Abstand der stabilisierten Axialpositionen des Nockenstücks auf der Trägerwelle.

Here are:

α _V

= Angle of rotation of the camshaft;

α _V0

= Angle of rotation of the camshaft, at which the cam follower begins to open the gas exchange valve with the elevation transmitted in the second axial position;

h _S

= momentary displacement of the cam piece with respect to the first axial position;

h _R

= axial distance of the stabilized axial positions of the cam piece on the carrier shaft.

Expressed in words, the invention consists in the always overlapping control times of the Axialkulisse and the gas exchange valve and concretely in that at least one of the cam lobes opens the gas exchange valve to a camshaft angle, which still within the Axialhubphase the shifting cam piece is located. This kinematic design makes it possible to substantially reduce the displacement of the Axialkulisse compared to known designs, wherein the displacement force which is required for the remaining Axialhub, is applied by the Rastiervorrichtung itself. This remaining Axialhub is covered in the course of one or more subsequent Grundkreisphasen until the cam piece is stably engaged in the second axial position. This stable state is typically achieved by immersing a spring-loaded by the carrier shaft detent ball in a detent contour in the cam piece, wherein an axial end stop for the cam piece can be formed by the detent contour alone or in common with surrounding components, such as the end faces of the cylinder head bearing points.

The reduced displacement can be used with unchanged long base circle phase to lower the axial acceleration of the Axialkulisse, or with unchanged high axial acceleration to shorten the base circle phase and thus to extend the gas exchange valve lift. Kinematically intervening embodiments are also possible.

Brief description of the drawings

Further features of the invention will become apparent from the following description and from the drawings, in which an inventive valve train is explained. Unless otherwise stated, the same or functionally identical features or components are provided with the same reference numbers. Show it:

1 a schematic lift diagram of a cam piece according to the invention;

2 a section of a known valve train in side view.

Detailed description of the drawings

The invention is based on 2 explained, which shows a variable-stroke valve drive of an internal combustion engine. The basic operating principle of this known valve train can be summarized to the effect that a conventional rigid camshaft formed by a camshaft 1 with an externally toothed carrier shaft 2 and on it by means of internal toothing rotationally fixed and longitudinally displaceable cam pieces arranged 3 is replaced. Each cam piece has two groups of axially immediately adjacent cams 4 and 5 on whose different Hubverläufe means cam follower, here by means of roller cam followers 6 selectively tapped and on gas exchange valves 7 be transmitted.

The operating point-dependent activation of the respective cam 4 or 5 required displacement of the cam piece 3 on the carrier shaft 2 via groove-shaped axial scenes 8th on the cam piece, which differ according to the direction of displacement in their orientation and in which, depending on the instantaneous axial position of the cam piece, in each case an actuating pin 9 an electromagnetic actuator (not shown) is coupled. To stabilize the cam piece in the two axial positions is a locking device which (not visible here) runs in the interior of the carrier shaft and engages in the interior of the cam piece.

This in 1 Diagram illustrated illustrates the axial relative movement of the cam piece 3 opposite the carrier shaft and the actuating pin 9 , For ease of reading of the diagram, the cam piece is axially stationary, and the relative movement is on the actuating pin and the cam follower in the form of the cam roller 6 projected. Plotted are the instantaneous displacement h _{S of} the cam piece and the stroke curve h _{V of} the gas exchange valves in dependence of the camshaft rotation angle α _V. The cam piece is through the two cams 4 and 5 symbolized, wherein the valve lift h _{V4 shown} by the solid line through the larger cam 4 and the valve lift h _{V5 shown} by the dashed line through the smaller cam 5 is produced. The cam roller is shown with a solid line in the two stable axial positions of the cam piece and with a dotted line at the camshaft rotation angle α _V0 in an intermediate position. In this intermediate position, the elevation-free base circle GK of the two cams ends, and the cam roller begins to transmit the valve lift h _V4 to the gas exchange valve.

The cam piece 3 In the two axial positions stabilizing locking device comprises a spring-loaded detent ball 10 , which is mounted in the carrier shaft and in the axial positions in inner latching recesses 11 and 12 of the cam piece engages. In each case shown is the stable state of the detent ball at the lowest points of the detent recesses, which are spaced by the dimension h _R. Reference for the instantaneous displacement h _{S of} the cam piece is the stable axial position that has just left the cam piece, hereinafter referred to as the first axial position.

The in the axial scenery 8th drawn circles symbolize the position of the coupled therein actuating pin 9 to different camshaft rotation angles α _V.

• a) Radiales Eintauchen des Betätigungsstifts 9 in die Axialkulisse 8, ohne die Nutflanken 13 und 14 zu berühren.
• b) Erstkontakt des Betätigungsstifts mit der Beschleunigungsflanke 13.
• c) Verschieben des Nockenstücks in Richtung der zweiten Axialposition aufgrund der Zwangsführung der Beschleunigungsflanke am Betätigungsstift.
• d) Infolge der Massenträgheit des Nockenstücks kontaktiert die Verzögerungsflanke 14 den Betätigungsstift 9; diese mit gepunkteter Linie dargestellte Position des Betätigungsstifts korrespondiert mit der Zwischenposition h_S0 der Nockenrolle 6 beim Ventilöffnungswinkel α_V0. Die mit gepunkteter Linie dargestellte Nockenrolle verläuft in dieser Grenzposition gerade noch bündig zum Nachbarnocken 5, ohne mit diesem während des nun beginnenden Ventilhubs h_V4 zu kollidieren. Für den momentanen Verschiebeweg beim Nockenwellendrehwinkel α_V0 gilt nun stets: h_S0 = h_S(α_V = α_V0) < h_R. In Worten ausgedrückt: der dynamische, d.h. durch Beschleunigungs-, Trägheits- und Reibungskräfte bedingte Verschiebeweg des Nockenstücks ist bei gerade beginnendem Ventilhub h_V4 immer kleiner als der axiale Abstand h_R der stabilisierten Axialpositionen. Dementsprechend befindet sich die Rastkugel 10 in dieser Zwischenposition noch vor dem stabilen, d.h. tiefsten Punkt der Rastmulde 11.
• e) Austauchen des Betätigungsstifts auf der radial ansteigenden Ausfahrrampe (nicht dargestellt) der Axialkulisse. Eine Verschiebung des infolge der Ventilbetätigungskräfte mit hohen axialen Reibkräften belasteten Nockenstücks erfolgt während der Übertragung der Ventilhübe h_V nicht oder allenfalls in einem nicht nennenswerten Umfang.

The sequence of dynamic displacement of the cam piece 3 in detail from left to right:

• a) Radial immersion of the actuating pin 9 into the axial scenery 8th , without the groove flanks 13 and 14 to touch.
• b) initial contact of the actuating pin with the acceleration edge 13 ,
• c) displacement of the cam piece in the direction of the second axial position due to the positive guidance of the acceleration edge on the actuating pin.
• d) Due to the inertia of the cam piece contacted the delay edge 14 the actuating pin 9 ; this dotted line position of the actuating pin corresponds to the intermediate position h _{S0 of} the cam roller 6 at the valve opening angle α _V0 . The dotted line cam roller runs in this limit position just flush with the neighboring cam 5 without colliding with it during the now starting valve stroke h _V4 . For the instantaneous displacement at the camshaft _rotation angle α _{V0, the} following applies: h _S0 = h _S (α _V = α _V0 ) <h _R. In other words, the dynamic displacement path of the cam piece, ie due to acceleration, inertia and frictional forces, is included just starting valve lift h _V4 always smaller than the axial distance h _{R of} the stabilized axial positions. Accordingly, there is the detent ball 10 in this intermediate position even before the stable, ie lowest point of the detent recess 11 ,
• e) dipping the actuating pin on the radially rising Ausfahrrampe (not shown) of the Axialkulisse. A displacement of the loaded due to the valve actuating forces with high axial friction forces cam piece is not during the transfer of the valve strokes h _V or at most to an insignificant extent.

In the second axial position is the detent ball 10 in its stable position at the lowest point of the detent recess 11 , and the cam roller 6 runs substantially axially symmetric to the cam 4 , The cam piece 3 force completely displaced into the second axial position results from the spring force of the locking device, which pulls the cam piece in the direction of this stable axial position during one or more load-free base circle phases GK.

LIST OF REFERENCE NUMBERS

1

 camshaft

2

 carrier wave

3

 cam piece

4

 cam

5

 cam

6

 Cam follower / cam roller

7

 Gas exchange valve

8th

 axial slotted

9

 actuating pin

10

 detent ball

11

 catch recess

12

 catch recess

13

 acceleration edge

14

 delay edge

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004008670 A1 [0002]
• DE 10148177 A1 [0003]

Claims (1)

Valve train of an internal combustion engine, comprising: - a camshaft ( 1 ) with a carrier wave ( 2 ) and a cam piece ( 3 ) placed on the carrier shaft ( 2 ) is rotationally fixed and slidably disposed between at least two axial positions and the cam group of immediately adjacent cams ( 4 . 5 ) with mutually different elevations and a groove-shaped axial backdrop ( 8th ), and with a Rastiervorrichtung ( 10 . 11 . 12 ), the axial positions of the cam piece ( 3 ) on the carrier shaft ( 2 ) stabilized; An actuator with one in the axial slide ( 8th ) engageable actuating pin ( 9 ) for moving the cam piece ( 3 ); - and a cam follower ( 6 ), which selectively picks up the surveys and a gas exchange valve ( 7 ) transmits; characterized in that during the dynamic displacement of the cam piece ( 3 ) from the first to the second axial position always has the following relationship: h _S (α _V = α _V0 ) <h _R α _V = angle of rotation of the camshaft ( 1 ); α _V0 = angle of rotation of the camshaft ( 1 ), in which the cam follower ( 6 ), the gas exchange valve ( 7 ) to open with the survey transmitted in the second axial position; h _S = instantaneous displacement of the cam piece ( 3 ) with respect to the first axial position; h _R = axial distance of the stabilized axial positions of the cam piece ( 3 ) on the carrier shaft ( 2 ).

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