WO2009003840A2 - Cam follower for a valve drive of an internal combustion engine - Google Patents

Abstract

A cam follower (2) is proposed for a valve drive (1) of an internal combustion engine with a lifting disc valve (9), to the shaft end face (8) of which at least two different valve strokes can be applied via a contact face (7) of the cam follower (2). The contact face (7) has a profile which is curved convexly in the longitudinal direction of the cam follower (2) and has at least one profile point (P0) from which two contact areas (K1, Kx), having profiles which are different from one another and are respectively adapted to one of the valve strokes, proceed. In this context, at least one of the contact areas (K1, Kx) is intended to have a profile with a continuously changing curvature, wherein the curvatures of the contact areas (K1, Kx) at the profile point (P0) are essentially of the same size.

Description

 Name of the invention

Drag lever for a valve train of an internal combustion engine

description

Field of the invention

The invention relates to a drag lever for a valve train of an internal combustion engine with a Tellerhubventil whose shaft end surface is acted upon by a contact surface of the rocker arm with at least two different valve strokes. In this case, the contact surface has a convexly curved in the longitudinal direction of the drag lever profile with at least one profile point, emanating from the two contact areas with mutually different and each adapted to one of the valve lifts profile curves.

Background of the invention

Such a finger follower is known from DE 10 2004 049 836 A1, which is regarded as generic. The rocker arm proposed there has a contact surface for actuating the disk lifting valve whose profile is composed of two circular-arc-shaped contact areas with radii of different sizes. The first large radius contact area is adapted to a conventional valve lift transmitted from the cam of a camshaft to the Tellerhubventil, while the second small radius contact area is adapted to a deactivated valve lift. This deactivated valve lift or valve zero stroke is produced by the fact that the stroke predetermined by the cam is not transmitted to the plate-lift valve, but is absorbed by a switchable support element which supports the cam follower. The disclosed in the cited document contact surface with two different radii ranges has the favorable property that the kinematic and hydrodynamic contact relationships between the contact surface of the finger lever and the shaft end surface of the Tellerhubventils largely independent of additional factors resulting from the changed Ventiltriebskinematik with deactivated valve lift, optimally can be adjusted. These influencing variables are, in particular, the contact between the contact surface of the drag lever and the shaft end surface of the disk stroke valve which migrates in the longitudinal direction of the drag lever or, in short, the so-called emigration. Taking into account the sometimes considerable component tolerance chains within the valve train, however, the known contact surface with two different but constant radii over the respective contact area and correspondingly constant curvatures can be disadvantageous in that the profile point does not start with the actual radii / curvature Contact point on the contact surface during the stroke-free base circle phase of the cam coincides. Starting from the base circle phase, the profile change between the contact regions as a result of a bending jump would then lead to abruptly changing contact conditions between the drag lever and the Tellerhubventil in the course of the lifting phase of the cam. In addition to undesirable vibration excitations of the valve train, the aforementioned deviation of the profile point from the actual contact point can also be accompanied by undesired contact pressures. This is the case, for example, when at the beginning and at the end of a large valve lift the contact area with a small radius and a correspondingly large curvature is in engagement with the shaft end surface of the plate-lifting valve. Object of the invention

The present invention is therefore the object of a drag lever of the type mentioned in such a way that the disadvantages mentioned are eliminated with simple means and in terms of manufacturing costs of the rocker arm substantially cost neutral.

Summary of the invention

The solution of this problem arises from the characterizing features of claim 1, while advantageous developments and refinements of the invention are the dependent claims can be removed. Accordingly, it is provided that at least one of the contact regions has a profile profile with a continuously variable curvature, wherein the curvatures of the contact regions at the profile point are substantially the same size.

By such a profiled contact surface can in the profile point as a starting point to the contact areas a kinematic jerk-free, i. significantly smoother profile change can be achieved than is possible in the case of the known contact surface with different, but partially constant radii / curvatures. In other words, the so-called jerk in the profile point, which is unavoidable in a curvature jump due to the coincidence of different radii, can be effectively eliminated.

The advantageous effects of the invention are particularly noticeable with increasing component tolerances of the valve gear according to a relatively large deviation of the profile point from the actual contact point noticeable, since on the one hand the gentle profile change leads to no inadmissibly high vibration excitation in the valve train and on the other in the vicinity of the profile point a small curvature both contact areas in favor of low contact pressures can be provided. In a further development of the invention, it is provided that the contact region with continuously variable curvature has a logarithmic profile profile K (x) = Ci * In [1 / (1-C ₂ * x ^a )]. In this case, Ci and C ₂ are constants, x coordinates the profile originating from the profile point in the longitudinal direction of the finger lever, and the exponent a is a real number. By means of these, with regard to the natural logarithm specific and with regard to the variable parameter generic profile description of the contact area, the expert in the field of valve actuators is an useful tool in useful technical and mathematical optimization tool for Profilge- the contact surface of the finger lever is given to hand.

Deviating from the Euler number e as the basis of the natural logarithm, any other basis for the mathematical description of profile curves is conceivable, by means of which suitable mechanical, kinematic and tribologically suitable contact conditions for the shank end surface of the plate-lifting valve in conjunction with adapted parameters in the sense of the invention to let.

In addition, it is provided that at least one of the contact areas has a circular arc-shaped profile profile with a constant curvature. In this regard, it can be particularly advantageous if exactly two contact areas are provided, wherein the contact area with constant curvature is adapted to an activated valve lift and the contact area with continuously variable curvature to a deactivated valve lift. Particularly in this case, it is expedient if the contact region with variable curvature has an overall steeper profile than the contact region with constant curvature. As with the kinematic design of valve trains with only one valve lift generally common, the contact surface can then contact the shaft end face also eccentric during the base circle phase of the cam -ideally at Profilpunkt- so that the proven kinematic and tribological contact conditions are maintained with activated valve lift, while at deactivated valve lift which then opposite running emigration of the contact surface on the shaft end surface can be kept very small.

As an alternative to the above-mentioned contact region with constant curvature, however, it is also possible to provide both contact regions with continuously variable curvatures of the same profile profile and to adapt these to the activated valve lift or the deactivated valve lift, respectively.

Another possibility consists in a reversed assignment of the contact areas to the different valve lifts. Accordingly, it can also be provided to adapt the contact region with continuously variable curvature to the activated valve lift and the contact region with constant curvature at a comparatively small radius to the deactivated valve lift.

Brief description of the drawings

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

1 shows a valve train of an internal combustion engine with a drag lever according to the invention in longitudinal section;

Figure 2 is a provided for the valve gear according to Figure 1 switchable

Supporting element and

3 shows a profile view of the contact surface of the finger lever according to FIG. 1 Detailed description of the drawings

FIG. 1 shows a valve drive 1 of an internal combustion engine with a drag lever 2, which is mounted in a manner known per se at one end on a support element 3 stationarily arranged in the internal combustion engine and has a rotatable roller 4 for tapping a cam 5 of a camshaft. The non-cutting formed here of sheet metal drag lever 2 has at the other end a transverse web 6 with a contact surface 7 for the shaft end surface 8 of a spring-loaded in the closing direction Tellerhubventils 9. As can already be clearly seen in FIG. 1 and will be explained in detail with reference to FIG. 3, the contact surface 7 has a convexly curved profile in the longitudinal direction of the drag lever 2, which comprises two contact regions with mutually different profile progressions. The design of the contact surface 7 makes it possible for the drag lever 2 according to the common-part principle not only in conjunction with the conventional, non-switchable support element 3, but also in conjunction with a switchable support element 10, as in the prior art in various embodiments known and is shown as an example in Figure 2, to use. In other words, it may be provided to equip the valve drive 1 of the internal combustion engine with identical drag levers 2, which are partly supported on non-shiftable support elements 3 and partially on switchable support elements 10, so that only a portion of the plate lift valves 9 is subjected to a variable valve lift is.

In the case of the switchable support element 10, the variable valve lift is a valve lift or valve zero stroke that is completely deactivated as a function of the operating point by interrupting the transmission of the cam lift to the plate lift valve 9. In this operating state, the cam lift is actuated by the switchable support element 10 with the rocker arm 2 then pivoting in the opposite direction added. The function and structure of the known switchable support element 10 can be summarized at this point to the effect that the switchable support element 10 in a housing 11th against the force of a lost-motion spring 12 longitudinally movably mounted pivot bearing 13 for the finger lever 2 and a hydraulically actuated locking mechanism 14 here by which a formschlüssü sig acting support of the pivot bearing 13 in the outer housing 11 can be produced or solvable bar.

The profile of the contact surface 7 is shown greatly enlarged in Figure 3 in diagram form. In this case, the orientation of the contact surface 7 shown in Figure 1 was maintained, ie the right side of the ordinate y and designated K _x designated contact area facing the roller 4 and the left side of the ordinate y shown and a circular arc profile profile with radius Ri having contact area K ₁ the role 4 turned away. The zero point of the abscissa x corresponds to a profile point P ₀ , from which the two contact areas K _x and K ₁ emanate, where x indicates the distance coordinate of the profile point P ₀ in mm. Compared to a thin line also drawn reference region K ₂ with circular arc profile profile and radius R ₂ according to the cited prior art, the contact area K _{x has} a natural logarithmic profile course K (x). Geometrically, this profile curve K (x) corresponds to the design formula given at the top left of the diagram with the parameters C ₁ , C ₂ and a specified below.

Compared to the reference region K ₂ , whose curvature is by definition 1 / R ₂ , the contact region K _x according to the invention has a significantly smaller curvature in the vicinity of the profile point P ₀ , which at the profile point P ₀ with the curvature 1 / R _{1 of} the contact region K ₁ is essentially identical. This fact is clarified in the additional detailed diagram placed on the ordinate, which highlights the profile profiles of the contact areas K ₁ , K _x and K ₂ at profile point P ₀ according to detail Z. The contact region K ₁ with radius R ₁ extending on the left side of the ordinate and the contact region K _x with logarithmic profile profile K (x) have the substantially identical curvature 1 / R ₁ at the profile point P ₀ , while the curvature 1 / R ₂ of the reference region K _{2 is} significantly greater and at the profile point P ₀ to a jerk due to the Krüm- would lead. Consequently, in the case of the operative rolling-sliding movement of the contact surface 7 on the shaft end surface 8, a gentle, ie kinematically jerk-free transition between the contact regions K ₁ and K _x results if the profile point P ₀ does not occur during the base circle phase of the cam due to component tolerances 5, but only in the course of its stroke phase comes into engagement with the shaft end surface 8. Depending on the position of the component tolerances, ie the deviation of the profile point P ₀ from the actual contact point during the base circle phase of the cam 5, this situation applies either to the activated valve lift or to the deactivated valve lift.

A further advantage of the contact surface 7 profiled in this way relates to the surface pressures in contact when the valve lift is activated, since the contact region K _{x of} variable curvature at the profile point P ₀ and in its vicinity has a significantly smaller curvature than the reference region K ₂ . Consequently, in the case in which the profile point P ₀ only comes into effective engagement with the shaft end surface 8 during the activated valve stroke, the contact region K _{x would also be} exposed to the then high contact forces due to valve acceleration and valve spring force. However, due to the comparatively low curvature of the contact region K _x in the vicinity of the profile point P ₀ , the corresponding contact pressures can be kept at the same low level which sets in the contact region K ₁ with a circular arc profile profile and comparatively low curvature 1 / R ₁ .

As already explained at the beginning, the contact region K _x with a variable curvature has an overall steeper profile than the circular-arc-shaped contact region K ₁ . The correspondingly small and initially in the direction of the roller 4 running emigration of the contact surface 7 on the shaft end face 8 is thereby kept very small when the valve is deactivated. As is generally customary in the kinematic design of valve drives with only one valve lift, consequently, the profile point P ₀ can also exaggerate the end surface 8 of the shaft. and offset here to the roller 4 during the base circle phase of the cam contact 5, so that the proven kinematic and tribological contact relationships between the contact surface 7 and the shaft end surface 8 are maintained when the valve is activated.

List of reference numbers

1 valve train

2 rocker arms

3 support element

4 roll

5 cams

6 crossbar

7 contact surface

8 shank end surface

9 disc lift valve

10 switchable support

11 housing

12 Lost motion spring

13 pivot bearings

14 locking mechanism

K _x contact area with variable curvature K ₁ contact area with constant curvature

K ₂ reference range

P ₀ profile point

Ri Radius of the contact area with constant curvature

R ₂ radius of the reference range

Claims

claims 1. drag lever (2) for a valve train (1) of an internal combustion engine with a Tellerhubventil (9), the shank end surface (8) via a contact surface (7) of the finger lever (2) with at least two different valve strokes can be acted upon, wherein the contact surface (7 ) has a convexly curved in the longitudinal direction of the finger lever (2) profile with at least one profile point (P ₀ ) from the two contact areas (K ₁ , K _x ) with mutually different and each adapted to one of the valve strokes profile curves, characterized in that at least one of the contact areas (K ₁ , K _x ) has a profile profile with a continuously variable curvature, wherein the curvatures of the contact areas (K ₁ , K _x ) at the profile point (P ₀ ) are substantially equal. 2. drag lever (2) according to claim 1, characterized in that the contact region (K _x ) with continuously variable curvature has a logarithmic profile profile K (x) = C ₁ * In [1 / (1 - C ₂ * x ^a )] , where C ₁ and C ₂ are constants, at x those from the profile point (P ₀ ) in Length direction of the finger lever (2) outgoing profile coordinate and the exponent a is a real number. 3. drag lever (2) according to claim 1, characterized in that at least one of the contact areas (K ₁ , K _x ) has a circular arc-shaped profile profile with constant curvature. 4. drag lever (2) according to claim 3, characterized in that exactly two contact areas (K ₁ , K _x ) are provided, wherein the contact region (K ₁ ) with constant curvature to an activated valve lift and the contact area (K _x ) are adapted to a deactivated valve lift with continuously variable curvature.