Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
2000-10-19
2001-11-20
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090570
Reexamination Certificate
active
06318322
ABSTRACT:
BACKGROUND
The invention relative to a valve drive of an internal combustion engine with the following characteristics:
a) the valve drive includes of a hydraulic support element, a finger lever and a cam of a camshaft or a plurality of these structural parts;
b) the support element is installed with its housing into a cam-side bore of a cylinder head, whereby a pressure piston that is axially movable relative to the housing and located in a bore of the housing projects with its head beyond the cylinder head in the direction of the cam, whereby between a bore-side bottom of the housing and a bore-side web of the pressure piston, a high pressure chamber for a hydraulic medium is located, which high-pressure chamber can be closed by a closing body of a check valve attached to the web in the direction toward a supply chamber or a supply line enclosed by the pressure piston;
c) the finger lever is constructed like a beam and has lateral surfaces near the cam and away from the cam, whereby it acts via a first end of the lateral surface away from the cam on at least one gas exchange valve in the direction of the stroke and is supported via a second end of the lateral surface away from the cam on the head of the pressure piston so that it can move by pivoting;
d) the cam acts on a contact section that lies between the ends of the cam-side lateral surface of the finger lever.
A valve drive of this type is known from the prior art from the document “Hydraulic Valve Lash Adjustment” (page 9) from August 1996, published by the applicant. It is disadvantageous in this that eccentricity of the cam base circle, transverse oscillations of the camshaft, brought on for example by auxiliary cams for injection pumps, or camshaft bearing play in the base circle can cause the high pressure chamber of the hydraulic support element to become hardened and the gas exchange valve opens in a most unfavorable way. Even in so-called transient operation of the engine, in particular during extremely cold environmental temperatures, the fall rate of the hydraulic support element is not sufficient to compensate for the positive dilatations on the gas exchange valve involved, preferably the outlet valve. In addition, in hydraulic support elements that have been constructed until now, a closing structure of its check valve must be opened with motor oil pressure. Thus, a certain time delay until the completion of the play compensation must be taken into account. This delay is a function of the instantaneous differential pressure incident on the check valve.
The object of the invention is thus to create a valve drive of the above-mentioned type, in which the cited disadvantages are eliminated.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved in that the valve drive is provided with opening mechanisms for the positive or compulsory opening of the check valve of the support element during contact of a base circle of the cam on the lever.
By these measures and in particular in combination with the mechanisms disclosed, the disadvantages cited at the beginning are effectively eliminated.
By the fact that positive opening is done in the base circle of the closing body of the check valve via the slide, the high pressure chamber is no longer hardened when the operating conditions described above occur. During the defined base circle window, an unhindered overflow by hydraulic agent from the high pressure chamber into the supply chamber (or the supply line), and vice-versa, is enabled. It is also successful to design the spring element for the closing body of the check valve so that it is clearly stronger in its force than spring elements designed previously for support elements until now. This improves the dynamic behavior of the support element.
The opening mechanisms are preferably formed out of the aforementioned slide for the closing body, which can be impinged by a separate lever. This lever in turn communicates with at least one signal path provided on the cam. In particular, the signal path is positioned as a component of the opening mechanism on the cam axially adjacent to it and is designed with an approximately circular shape. In this manner, preferably on both sides, edge areas of the base circle of the cam and preferably, but not necessarily, the remaining path section outside of the base circle (cam catch flank, cam peak, cam drop flank) can be set at a lower radius than the base circle window. Thus, the slide is moved over the signal path that is raised in the base circle, which acts on the separate lever, moving it in such a way in the bore direction of the support element that the closing structure is opened forcibly and prevented from closing.
Edge areas of the base circle, which border on the cam catch flank and cam drop flank, are therefore designed lowered in radius so that the fill valve lift is available when the closing body for the gas exchange valve is closed. Otherwise, the loss in lift must be compensated by an increased cam contour.
In a preferred embodiment, a two-piece slide is proposed, which preferably has a rod-like construction. Also conceivable, however, are other geometries and/or also non-axially running slides, but rather these types of mechanisms acting radially or slanted on the closing body. Likewise, triggered external impingement mechanisms such as electromagnets and the like can be used to dislocate the closing body during the base circle phase.
According to an advantageous embodiment of the invention, the separate lever should be attached on the second end of the finger lever. A simple attachment form is created in that the lever has in the section of the end, a bent projection which has a clip. Using this clip, it can be attached in a simple way to the second end of the finger lever. As an alternative to this, it is also contemplated to insert a joint as a bearing for the second lever and/or to arrange the second lever separately relative to the cylinder head or an additional structural part arranged in the cylinder head.
A measure favorable in terms of wear is provided in an additional subordinate claim. According to the measure, the separate lever should be expanded in its contact area to the signal path or to the slide or provided with suitable wear protection measures such as a heat treatment. In this way, the life of the lever is clearly improved or its wear is reduced. If possible, this separate lever, as well as the finger lever as such, can be dimensioned so that it is thin-walled or made from a light construction material.
A first part of the proposed two-piece slide runs advantageously in the second end of the finger lever, whereby the finger lever has as a rest for the head of the pressure piston of the support element, a dome-shaped recess. The first part is spring-loaded in the cam direction via a spring element, such as a compression spring. Thus, in the unloaded state of the signal path, the first part is removed via the spring element from the area of the dome-shaped recess. In this way, the first part can no longer come into contact with the head of the pressure piston when the finger lever is pivoted. At the same time, the second part of the slide, which is adjacent to the first part, is made so that its length is such that it also does not project into the area of the dome-shaped recess when it is unloaded, so that it has a contact to the base of this recess.
In a further embodiment of the invention, it is proposed to guide the second part of the slide over a head of the pressure piston, which is constructed so that it is solid, for example, where the pressure piston then has a longitudinal bore. It can be provided, however, also, to arrange inside the pressure piston, preferably in this supply chamber, a separate washer or a similarly suitable mechanism, over which the second part is additionally conducted. Should the pressure piston not be constructed so that it is solid, but instead, for example, from a sheet metal material, then in the head area, separate sheaths or similarly used elements can be applied. Also, it is concei
Ina Walzlager Schaeffler OHG
Lo Weilun
Volpe & Koenig P.C.
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