Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
1999-10-29
2001-07-03
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090410, C123S090420, C074S559000
Reexamination Certificate
active
06253721
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention involves a swivel mounted cam follower of a valve drive of an internal combustion engine having the following characteristics:
a) the cam follower has thin walls and is constructed in a finger shape and has selectively parallel side walls with a crosspiece connecting them;
b) the side walls form with the crosspiece, at least in the area of the ends of the cam follower, a profile having a U-shaped cross-section and they enclose an intermediate space;
c) the cam follower acts at one end via an underside of the crosspiece on a shaft end of a gas exchange valve and
d) two spaced apart straps extend from the end and the shaft end of the gas exchange valve is guided between them.
A cam follower of this general type is known from the patent EP-PS 05 73 674. It is disadvantageous in this cam follower that it has a separate insert piece in the area of the tightly fitting valve shaft (see FIG.
1
). This increases in a disadvantageous way the manufacturing expense in making this type of cam follower. In addition, it is designed to be relatively wide. For this reason, it has a comparatively large mass and thus an unfavorable mass moment of inertia. This unnecessarily increases the valve drive friction.
The insert piece described above has only a relatively small guide height for the tightly fitting valve shaft. It would be desirable, for many applications, however, to have a larger guide height by which advantageously a falling down of the cam follower is prevented during its pre-mounted state in the cylinder head of the internal combustion engine or by which this cam follower is fixed in position extremely well during its use in the operating state of the internal combustion engine.
SUMMARY OF THE INVENTION
The purpose of the invention is thus to create a cam follower of the type described above, in which the cited disadvantages are eliminated and which can be manufactured in a simple manner especially having a small mass and at the same time guarantees an excellent guide of a shaft end of a gas exchange valve.
According to the invention, this purpose is achieved by providing a pivotable cam follower having the features noted below, which are used to improve this arrangement, and are an advance over the known cam followers.
According to the invention, the straps are constructed as an extension of the side walls that is bent by
180
° onto the underside, where the underside of the side walls is turned away from the intermediate space, and the side walls are, in the area of the end, minimized in their separation distance or taper in this area selectively in a conical manner, such that they are set off at equal separation distances outside of the end.
Since the side walls in the area of the end that covers a longest arc during pivoting, are minimized in their separation distance, a cam follower having a smaller mass and thus a smaller mass moment of inertia as well as a clearly higher rigidity in the area of the valve seat, than the cam follower known from the state of the art, is created. At the same time, the straps should be manufactured as an extension of the side walls, which proves to be especially favorable in production manufacturing. A guide height for the shaft end of the gas exchange valve to be enclosed can be determined by the selection of the length and width of the straps.
Of course, a cam follower is also included within the protective scope of this invention, which has side walls that are designed not necessarily at equal distances or having straps that are bent by an angle deviating by
180
° in the direction toward the underside.
In the further development of the invention, the cam follower is to be manufactured out of a sheet metal material, where, for example, it is manufactured from a blank by cold forming. A cam follower made out of a sheet metal material of this type proves to be relatively cost-effective. However, conceivably and included within the protective scope of this invention, are all other materials which can be made in the proposed shape, thus also plastics or fiber and/or particulate reinforced plastics are included.
In an advantageous way, the contour of the cam follower and thus also the contour of the straps are formed by blanking presses. If one were to shape the straps out of the cross-strap, their final geometry would have to be disadvantageously pressed later. Because of the shaping of the straps out of the side walls, smooth contact surfaces are present to guide the valve shaft, since no punch outline occurs in this area. Expensive reworking can be rendered unnecessary.
A simple measure for a connection of the straps with the underside of the cam follower is disclosed. According to it, each strap is to have a nub, or similar piece, bent at a right angle in the direction towards the underside. This nub is preferably formed during a punch operation of the cam follower and after a bending of the straps to the underside, it is welded to this underside.
Finally, it is proposed to position in the cam follower a roller set selectively in roller bearings as a component running counter to the cam. In this way, the friction in the valve drive is further minimized compared to the slide calipers used until now. However, a roller set in slide bearings or possibly a slide caliper would also be conceivable.
Since the straps are to be made having a height that is greater than the thickness ofthe sheet metal, an excellent guide for the valve shaft is possible because of the largely adjustable height.
As a cam follower, dragging, tilting or swinging levers are provided. These can also act on several gas exchange valves at the same time and thus be constructed, for example, in a finger or fork shape. Likewise, the cam follower can be inserted into a switchable lever drive, or this drive can have a hydraulic play compensation component.
REFERENCES:
patent: 5775280 (1998-07-01), Schmidt et al.
patent: 5979383 (1999-11-01), Faville et al.
patent: 6035820 (2000-03-01), Engelhardt et al.
patent: 6062184 (2000-05-01), Engelhardt et al.
Engelhardt Helmut
Mayer Wolfgang
Speil Walter
Ina Walzlager Schaeffler OHG
Lo Weilun
Volpe & Koening, P.C.
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