Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1994-11-29
1996-05-07
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9022, F01L 112, F01L 126, F01L 118, F01L 1300
Patent
active
055136028
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a valve-actuating mechanism for an internal-combustion engine.
BACKGROUND OF THE INVENTION
In a known valve-actuating mechanism of this type (EP-A-342,007), two coupling pins butting against one another are provided in the bores of the rocker arms and can be displaced counter to a spring force, by an electromagnet arranged in one of the rocker arms, in such a way that they bridge the separating gaps between adjacent rocker arms and thus connect all the rocker arms rigidly to one another, so that the rocker arms acting on the valves are now moved by the second rocker arms according to the cam contour of the second cams. One problem in this construction is that the coupling pins have to be positioned very accurately, in order to ensure that the first two rocker arms can move freely in the uncoupled position. Furthermore, accommodating an electromagnet, by means of which the necessary short switching times of approximately 5 ms can be achieved, in the rocker arm presents considerable problems as do the dissipation of the heat generated and the current supply. Finally, in the event of repair, the valve drive has to be at least partially dismantled.
SUMMARY OF THE INVENTION
The object on which the invention is based is to provide a valve-actuating mechanism of the relevant generic type, in which the first rocker arms can be connected to the second rocker arms or be separated from these in a simpler way by means of an electromagnetically actuable coupling device.
In the proposal according to the invention, the coupling device is a rotatable switching shaft which can extend outwards, so that the electromagnet can be arranged at a suitable point next to the switching shaft in the cylinder head, where there is, of course, more space than in a rocker arm and the dissipation of the heat generated presents no problems. A further advantage is that, if a defect occurs, the electromagnet can be exchanged easily, whereas, in such a case, an at least partial dismounting of the valve drive would be necessary in the known mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary embodiment of the invention is described below with reference to the drawings. In these:
FIG. 1 shows a valve drive with a valve-actuating mechanism according to the invention for three inlet valves in a vertical section along the line 1--1 in FIG. 2,
FIG. 2 shows a section along the line 2--2 in FIG. 4,
FIG. 3 shows a section along the line 3--3 in FIG. 2, the switching shaft being shown in the position according to FIG. 1,
FIG. 4 shows a section corresponding to that of FIG. 1, the coupling device being shown in a second position,
FIG. 5 shows a section corresponding to that of FIG. 3, the switching shaft being shown in the position according to FIG. 4, and
FIG. 6 shows a section along the line 6--6 in FIG. 2.
DETAILED DESCRIPTION
The drawings show a valve drive for three inlet valves 1, of which, however, only one is shown in FIG. 1. Each valve 1 is loaded in the closing direction by a spring 2. The valves are actuated by specific cams 3 of a camshaft 4 via rocker arms 5 which are mounted pivotably on a common axle 6 of fixed location. The cams 3 can have diffrent cam profiles for the individual inlet valves, in order to obtain a different valve stroke, a different opening duration and/or different control times and to afford optimum preconditions in the lower and medium speed range of the internal-combustion engine. Arranged on the axle 6 between adjacent first rocker arms 5 are second rocker arms 7 actuated by second cams 8 having an identical cam profile which is designed for the conditions in the upper speed range of the internal-combustion engine, that is to say, for example, brings about a larger valve stroke and a longer opening duration. The second rocker arms 7 have extensions which extend rearwards and on which is supported a spring 7a which endeavours to keep the second rocker arms bearing against their cams 8. The second rocker arms 7 can be coupled to the first rocker arms 5
REFERENCES:
patent: 5101778 (1992-04-01), Fukuo et al.
patent: 5251586 (1993-10-01), Koga et al.
patent: 5253620 (1993-10-01), Dohn et al.
Audi AG
Lo Weilun
LandOfFree
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