Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-04-09
1998-07-21
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 905, 123198F, F01L 114, F01L 124, F01L 1300
Patent
active
057822166
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a tappet for a valve drive of an internal combustion engine comprising an annular bottom portion arranged concentrically around a circular bottom portion, the annular bottom portion being loaded in stroke direction by at least one cam of higher lift than the circular bottom portion, and said annular and circular bottom portions being slidable relative to each other, the tappet being guided for longitudinal displacement in a bore of a cylinder head by a skirt connected to the annular bottom portion, while a cam-distal end surface of the circular bottom portion receives a guide bush which is at least partly and indirectly surrounded by a bore of the annular bottom portion, at least one radially displaceable first piston which serves as a coupling element for a selective positive coupling between the two bottom portions in a base circle phase of the cams being arranged in a region within or near the two bottom portions, and said first piston can be loaded in at least one direction of travel by a hydraulic medium and in an opposite direction of travel optionally by hydraulic medium or by a force of at least one spring, while, to establish a coupled state, said first piston overlaps a separating surface extending in axial direction between said two bottom portions.
STATE OF THE ART
In a tappet of the aforesaid type known from DE-A 42 06 166, a coupling between the two bottom portions is achieved by pistons which are displaceable radially inwards by a hydraulic medium. In this coupled state, the outer high lift cam acts on the tappet. This tappet is a compromise as far as its lifting curve is concerned. It enables either a maximum lift through the outer high lift cams or a low lift through the central cam. Thus it is possible to set a suitable valve lift curve for high and low engine speeds because, generally speaking, large valve cross-sections are only desirable at high engine speeds. On the other hand, it is desirable in multi-valve engines, to shut down a valve or complete rows of cylnders, for example in V-engines, so that the engine can be operated with notably reduced throttling losses at low load. However, this generic prior art document contains no suggestions as to a configuration of a valve drive tappet which would make it switchable between different valve lift curves, or between a zero lift curve and two different lift curves, and at the same time permit a complete valve shut-down with the help of the switching mechanism.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to improve a tappet of the generic type to eliminate the aforesaid drawbacks and provide a compact switching mechanism which enables coupling for three different valve lifts one of which permits the gas exchange valve concerned to remain completely closed.
DESCRIPTION OF THE INVENTION
The invention achieves this object by the fact that an inner piston is slidably arranged in a bore of the guide bush at a distance from the cam-distal end surface of the circular bottom portion, the opposite end surface of the inner piston cooperating at least indirectly with an end of a valve stem, and the inner piston comprises at least one radial bore for lodging a second piston which constitutes a coupling element which is displaceable in the base circle phase of the cams optionally by hydraulic medium or by the force of a spring. These measures of the invention permit the valve lift to be adapted to different engine speeds so that an optimum filling of the cylinder with the fuel-air mixture can be achieved. On the other hand, it is possible for the first time to simultaneously realize a third coupling or switching step which can be designed for a zero lift, if desired, so that, as described above, complete rows of cylinders can be shut-off while other cylinder rows are in operation. These measures are particularly advantageous in engines having six or more cylinders but can equally well be used in internal combustion engines with less cylinders.
With a suitable contour of the low lift cam, a small
REFERENCES:
patent: 5090364 (1992-02-01), McCarroll et al.
patent: 5361733 (1994-11-01), Spath et al.
patent: 5402756 (1995-04-01), Bohme et al.
patent: 5431133 (1995-07-01), Spath et al.
patent: 5555861 (1996-09-01), Mayr et al.
Haas Michael
Maas Gerhard
Speil Walter
Wollboldt Birger
INA Walzlager Schaeffler KG
Lo Weilun
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