Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-03-24
2001-05-01
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090480
Reexamination Certificate
active
06223706
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a tappet for a valve train of an internal combustion engine, designed to be coupled for different lifts of at least one gas exchange valve and comprising an outer annular section which concentrically encloses a circular section which is axially movable relative to said annular section.
BACKGROUND OF THE INVENTION
A tappet of the pre-cited type is known from DE-OS 196 22 174.
FIG. 8
of this document, for example, discloses a tappet having a coupling mechanism comprising in its annular section, two slides configured as pistons. Each of these pistons can be displaced toward the circular section by hydraulic means acting axially from the outside so that the entire tappet follows a lift of the cams which act on the annular section. To exclude switching errors, the outer cams possess a control contour that cooperates with locking means (balls) on the outer peripheral surface of the pistons. These pistons comprise axially spaced annular grooves. At the end of a base circle phase of the cams, the balls are displaced into these grooves by the control contour. An axial movement of the pistons is thus prevented.
A drawback of this prior art is that the locking means are situated in the region of the hydraulic medium supply to the pistons. This can result in hydraulic medium losses or make it problematic to implement sealing measures in this region. At the same time, due to their stiffness, these balls can get seated on an annular shoulder between the annular grooves of the pistons when a command to lock has been triggered by the control contour. This occurs when the pistons are not sufficiently displaced and can lead to a loading or even destruction of the component.
SUMMARY OF THE INVENTION
The object of the invention is therefore to create a tappet of the pre-cited type in which the mentioned drawbacks are eliminated and in which, more particularly, the locking means are spatially separated from the hydraulic medium supply to the slides, and, at the same time, to create locking means that yield in a cam-distal direction.
These and other objects and advantages of the invention will become obvious from the following detailed description.
A tappet switchable to different valve lifts is created in which switching errors of the slides are efficiently prevented. Due to the fact that the locking means are spatially separated from the prevailing hydraulic medium pressure for displacing the slides, the aforesaid hydraulic medium losses are no longer to be expected. At the same time, the transmitting members of the locking means are supported on a compression spring which urges the annular section in cam direction. In this way, a locking means is created that reliably yields in a cam-distal direction. A particular advantage of the invention is also that the transmitting members are situated outside of a reception for the associated slide.
The corresponding locking member is advantageously wedge-shaped in its region of engagement on the slide which comprises locking recesses of complementary shape to this wedge shape. Thus, in case of incomplete displacement, the first slide is moved into one of its end positions by wedge effect.
Due to the fact that the locking member is mounted on a compression spring which surrounds the circular section, a certain yielding of the locking member is achieved for the extremely rare case that a peak of the locking member and the annular shoulder situated between the annular grooves of the first slide come into confronting positions at a time when the signal track (control contour) is effecting a locking of the first slide. In place of the compression spring, it is also possible to provide a separate spring means for the locking means in axially parallel relationship to the tappet.
When pressure medium pressure decreases, the compression spring which biases the first slide toward the further receptions displaces this slide into a position immediately in front of an annular surface between the sections. The compression spring surrounding the second slide assures in a simple manner, a central positioning of the second slide because, in the switched-off state of the tappet, the annular section can execute such a large differential stroke relative to the circular section that the reception of the second slide is completely exposed. The second slide may comprise a ring to serve as an abutment surface for the second compression spring. This ring may extend, for instance, in a peripheral groove of the second slide. However, it is also possible to make the end coils of this compression spring with a smaller diameter and arrange them in an annular groove of the second slide.
The bores of the rings arranged in the receptions of the sections provide in a simple manner, slide ways for the slides so that an expensive finishing of the actual receptions in the sections is not required. The rings in the annular section can be used at the same time to provide axially outer closures for the receptions. The closure on the side of the first slide advantageously comprises an opening through which air displaced during a displacement of the first slide can escape. The closure of the second ring additionally serves to delimit a hydraulic medium chamber situated in front of the second slide. It is further proposed to stamp a region of a cylindrical wall of the ring for the second slide radially inwards. This forms an axial outer stop for the second slide in its reception.
It is proposed to equip the tappet with a hydraulic clearance compensation element. In this case, separate supplies of hydraulic medium to the slides and the clearance compensation element starting from inlets in the skirt of the tappet are provided. As seen in a top view of the tappet, a reservoir is arranged on one side next to each reception.
To act on the locking member configured as a pin, the signal track of the cam situated opposite thereto can be configured as a groove except for a first part of its base circle. When the recessed part of the signal track beginning with a second part of the base circle runs on the pin, this pin is simply pushed by the compression spring loading it into the groove. In this way, a displacement of the first slide is reliably prevented because the pin engages the opposing locking recess of the slide.
In place of the signal track configured as a groove, the first part of the base circle of the cam may also comprise an elevation protruding from the rest of the cam contour.
REFERENCES:
patent: 5782216 (1998-07-01), Haas et al.
patent: 5950583 (1999-09-01), Kraxner et al.
patent: 196 22 174 (1997-06-01), None
patent: 2162246 (1986-01-01), None
Maas Gerhard
Schnell Oliver
Bierman, Muserlian and Lucas
Ina Walzlager Schaeffler OHG
Lo Weilun
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