Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1994-10-13
1995-11-07
Yuen, Henry C.
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 904, F01L 112, F01L 118, F01L 126
Patent
active
054639883
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a valve actuating mechanism for an internal combustion engine.
BACKGROUND OF THE INVENTION
In a state-of-the-art valve actuating mechanism of this type (EP-A 213 759 or GB-A-2199894) connection between the first and the second set of rocker arms in the higher speed range is effected by means of pistons displaceable by oil pressure which are mounted radially to the swivel axis of the rocker arms in bores provided in the rocker arms. The bores are aligned with each other when the rocker arms rest on the base circles of their cams. In the lower speed range, in which the valves are to be actuated by the cams associated with the first set of rocker arms, the frontal surfaces of the meeting pistons are situated in the division planes between the rocker arms, so that the valves are actuated exclusively by the first set of rocker arms and the second set of rocker arms can swing freely. In the upper speed range the pistons are displaced in such a way that they penetrate the division planes, with the result that the second set of rocker arms is connected to the first set of rocker arms and the valves are actuated by the second set of rocker arms as determined by the outline of the cams associated with the second set of rocker arms. Different valve lifts and different open periods can accordingly be produced in the higher and the lower speed ranges. One disadvantage of the state-of-the-art design is that in the lower speed range the frontal surfaces of the pistons continually slide into each other and that very high precision is required in manufacture of the pistons and the bores.
SUMMARY OF THE INVENTION
It is an object of the invention to create a valve actuating mechanism of the state-of-the-art type in which wear is reduced and the manufacture of which is simplified.
It is proposed on the basis of the invention that the pistons be retained by springs in the lower speed range so that no contact takes place with the second set of rocker arms. Since no bores are provided in the second set of rocker arms that must come into alignment with the bores in the first set of rocker arms if the valves of the first set of rocker arms are to be actuated by the second set of rocker arms, manufacture is significantly simplified. End facing of the bottom of the crosspiece is all that is required.
Because of manufacturing considerations, the bores and the pistons in the first set of rocker arms are preferably circular in cross-section. The end sections of the pistons, which in the higher speed range operate in conjunction with the bottom of the crosspiece, have a plane surface, as a result of which two-dimensional contact between piston and crosspiece is effected and the surface pressure is correspondingly reduced. In order to make certain that the plane surfaces of the end sections are at all times positioned parallel to the bottom of the crosspiece, it is preferable to provide protection against rotation of the piston that can simultaneously limit the outward movement of the piston.
BRIEF DESCRIPTION OF THE DRAWINGS
An example of an embodiment of the invention is described as follows with reference to the drawings, in which:
FIG. 1 shows a valve drive with a valve actuating mechanism in accordance with the present invention for three inlet valves, in the vertical section along line 1--1 in FIG. 2, and
FIG. 2 presents a view in the direction of arrow 2 in FIG. 1.
DETAILED DESCRIPTION
A valve drive for three inlet valves E is shown in the drawings. A spring 1 applies pressure to each valve E in the direction of closing. The valves are actuated by cams 2, 3, and 4 of a camshaft 5 by way of a first set of rocker arms 6 rotatably mounted on a common stationary shaft 7. The cams 2, 3, and 4 preferably have different cam profiles so as to achieve a different valve lift for the individual inlet valves, a different open period, and/or different control times in order to achieve optimum preliminary conditions in the lower and medium speed ranges of the internal combustion engine. Mounted between adjac
REFERENCES:
patent: 4844023 (1989-07-01), Konno et al.
patent: 5042437 (1991-08-01), Sakuragi et al.
patent: 5207193 (1993-05-01), Sugimoto et al.
patent: 5388552 (1995-02-01), Sugimoto et al.
Audi AG
Lo Weilun
Yuen Henry C.
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