FIELD OF THE INVENTION

[0001] The invention concerns a finger lever of a valve train of an internal combustion engine, said finger lever being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever having two arms between which an inner lever is arranged for pivoting relative to the outer lever, which outer and inner levers can be coupled to each other by a coupling element so that, upon coupling, a high valve lift, and upon uncoupling, a low valve lift is generated, the finger lever further comprising on one end, a support for a gas exchange valve, on an opposite end, a complementary surface for a support element and on at least one of the outer and inner levers, a contact surface for a cam.

BACKGROUND OF THE INVENTION

[0002] In a finger lever of the pre-cited type disclosed in DE-OS 27 53 197, the inner lever cooperates with a high-lift cam and the outer lever cooperates with a pair of low-lift cams. The surfaces for contacting the cam are sliding contact surfaces. A drawback of this prior art is that the sliding contact surfaces unnecessarily increase friction in the valve train.

[0003] It is usual, in general, in finger levers of the pre-cited type to equip only the inner lever with a roller that constitutes a contact surface for the cam and to provide a sliding contact surface on the arms of the outer lever. Generally, the inner lever cooperates with a high-lift cam and the outer lever is contacted by a low-lift cam and possesses, for example for reasons of design space, only sliding contact surfaces on the arms. However, empirically or statistically seen, the switchable finger lever is switched for 80 to 90% of the operating time of the internal combustion engine to the low lift so that it is the outer lever that is activated. Thus the relatively low-friction roller contact is availed of only for a short period of operation. This means that for a major portion of the operation period, the inner lever comprising the roller as a cam contacting surface executes a lost motion and the roller with its comparatively large mass oscillates unnecessarily in the valve train.

OBJECT OF THE INVENTION

[0004] The object of the invention is therefore to provide a finger lever of the pre-cited type in which the aforesaid drawbacks are eliminated.

SUMMARY OF THE INVENTION

[0005] According to a first solution, the invention achieves the above object by the fact that only that one of the outer and inner levers that, empirically or statistically seen, predominantly transfers the cam lift to the gas exchange valve during the operation of the internal combustion engine comprises a rotatable roller acting as a cam contact surface.

[0006] Alternatively, according to a second solution, the invention achieves the above object by the fact that the outer lever is configured to transfer a high cam lift and the inner lever is configured to transfer a low cam lit, and only the inner lever comprises a rotatable roller acting as a cam contacting surface while each arm of the outer lever comprises a sliding contact surface acting as a cam contacting surface.

[0007] In this way, the aforesaid drawbacks are effectively eliminated. It is understood that further features of the invention that will be described below can be incorporated in both solutions. It is also conceivable to achieve only a zero lift through the inner lever so that the valve is de-activated, or to achieve a minimum lift.

[0008] Thus, only that lever that during normal operation of the internal combustion engine predominantly transfers the cam lift comprises the roller acting as a cam contacting surface. Preferably, this lever is the inner lever and the roller is preferably mounted on the pin through a rolling bearing such as a needle roller bearing. Sliding contact surfaces are provided as cam contacting surfaces on the arms of the outer lever for the high-lift cam. In this way, a low-friction cam contact is achieved in the main operation range of the internal combustion engine (low load to part load) in which only a small valve lift is desired.

[0009] According to a further feature of the invention, one end of the inner lever comprises the support for the gas exchange valve and the opposite end of the inner lever comprises a complementary surface for mounting on a preferably hydraulic support element. This complementary surface can particularly be configured as a cup-shaped recess on the inner lever. This enables a simple pivoting motion of the finger lever on the support element.

[0010] The coupling element is constituted by slides, not specified more closely, that can be displaced in at least one axial direction, for example hydraulically, electromagnetically or by the force of a compression spring. According to a still further proposition of the invention, an axial line of the slide coincides with an axial line for the roller in the inner lever. It goes without saying that the slides can likewise extend outside of an axial line of the roller. In place of the slides, it is also conceivable to use other coupling elements like latch- or ball-type elements and the like.

[0011] According to another proposition of the invention, in a region of the end of the inner lever comprising the support, the inner lever projects clearly beyond an end of the outer lever. In this way, the outer lever is configured only with a length that is absolutely necessary. This reduces the mass as well as the cost of manufacture of the finger lever.

[0012] A still further proposition of the invention concerns a simple connection of the inner lever to the outer lever. A pin or a similar component extends through the inner lever in a region of the opposite end, and the outer lever is pivotally mounted through its arms on this pin. Advantageously, at least one torsion spring acting as a lost motion spring is also arranged in the region of this pin. This torsion spring is supported at one end on a crossbar that connects the arms of the outer lever and, at another end, this torsion spring acts on a stop of the inner lever that is configured, for instance, as a pin and arranged on an outer wall of the inner lever. If necessary, other lost motion springs like coil springs and the like may also be used. It is also possible to mount the outer lever on the inner lever by other means, for example, through socket-like supports or a forked engagement.

[0013] If at least one part of the finger lever is made of a light-weight material like sheet metal or fiber-reinforced plastic, a further contribution is made to reducing both the weight and the oscillating mass of the valve train.

[0014] The invention will now be described more closely with reference to the appended drawing.