Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-03-05
1998-02-24
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9041, 123198F, F01L 1300
Patent
active
057202443
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a switchable support element for a cam-actuated finger lever of a valve drive for an internal combustion engine, having a hollow cylindrical housing disposed with its outer jacket in a receiving bore of a cylinder head, with a piston disposed therein which is axially movable at least relative to the housing and supported by a compression spring.
Such a device is known from DE-A 40 00 531, and includes also a hollow cylindrical housing connected together with a hollow cylindrical inner element and disposed inside a cylinder head of an internal combustion engine. Both elements are biased by a compression spring in direction of discharge. The housing is provided with an oil supply line for enabling in conjunction with a control edge of the inner element and in dependence on an oil charge in the inner space enclosed by the two elements a lifting/lowering of the inner element relative to the housing and to thereby shut down or vary the stroke of the gas exchange valve which communicates with the support element via the finger lever. The different oil charge is effected by turning the housing relative to the inner element, since thereby different inlet flow cross sections are provided via the control edge.
The valve drive tappet known from above-stated DE-A 40 00 531 has the drawback that the oil cushion does not allow a formfitting, i.e. a defined cutoff/decrease of the valve lift. This oil cushion exhibits, on the one hand, a certain minimum compressibility, and on the other hand, oil losses can be expected across the sliding surface of both elements. Furthermore, it is anyhow difficult to achieve a precise stroke adjustment and fixation in this position by means of oil pressure, since the adjusted height is maintained directly through the oil pressure, and too many additional parameters which are hard to manage have an impact. In addition, the housing must be acted upon by mechanical forces to effect a rotation so that again a drive is needed. Other operational condition may also be conceivable, by which the gas exchange valve can be activated when the internal combustion engine is shutdown, i.e. the valve should not be turned off. The above solution makes no provisions therefor, since the aforementioned adjustment device collapses when the internal combustion engine is shutdown, thereby deactivating the respective gas exchange valve.
There are other switchable support elements known in the art (DE-GM 93 19 435.8), which effect a locking of the components for coupling the support element to the stroke motion of the control cam via radially displaceable pistons. In the decoupled state, a respective housing part executes an idle stroke during lifting of the control cam.
SUMMARY OF THE INVENTION
It is the object of the invention to improve a switchable support element in such a way that it exhibits a high stiffness when its components are locked, while in the disengaged state previously encountered friction losses are minimized and, at the same time, the support element can be disengaged at high rotational speeds.
This object is attained according to the invention by disposing in the piston at least one bore extending radially or as a secant and aligned with a respective other bore during the base circle portion of the cams, with at least one coupling element being arranged in one of the bores and moveable in the direction of the respective other bore for selectively coupling/decoupling of the support element with the finger lever secured thereto from a stroke motion of the control cam; by providing in a cam-distal bore of the piston an inner element which is axially moveable with respect to the other bore, wherein a cam-proximal end face of the inner element is spaced at a distance during the base circle portion of the control cam and in coupled state of the support element relative to a base of the bore, at formation of a piston space, which distance corresponds to the desired cutoff stroke of the finger lever; by positioning the piston to rest with its
REFERENCES:
patent: 4546734 (1985-10-01), Kodama
patent: 4615307 (1986-10-01), Kodama et al.
patent: 5357916 (1994-10-01), Matterazzo
patent: 5501186 (1996-03-01), Hara et al.
Feiereisen Henry M.
INA Walzlager Schaeffler KG
Lo Weilun
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