Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1996-01-11
1997-07-29
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 905, 123 9055, F01L 1300, F01L 114
Patent
active
056513356
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention refers to a tappet for a valve actuating mechanism of an internal combustion engine having a circular ring shaped base section and a circular base section which are arranged concentrically to each other and respectively acted upon by cams of different strokes, with a central cam of small stroke acting upon the circular base section and at least one adjacent cam of greater stroke acting upon the circular ring shaped base section, wherein the tappet is guided in a bore of a cylinder head by a hollow cylindrical jacket that is connected to the circular ring shaped base section while the circular base section receives at its cam-distant end face a guide sleeve accommodating a clearance compensation element, and wherein the units which comprise the two base sections are slideable relative to each other and engageable by radially displaceable coupling means.
German Pat. No. DE-A-42 06 166 discloses a tappet of this type which includes a two-part housing with a base acted upon by at least two cams of different stroke pattern. Coupling of both housing parts is effected by pistons that act in radial direction and are provided with pins. In disengaged position, the outer housing part executes an idle stroke. The inner housing part follows the contour of the inner cam. The valve executes a smaller stroke. In case the tappet of this type should act hydraulically in order to compensate a possibly existing valve clearance, it is not possible or only at great difficulty to effect the oil supply to the hydraulic element. In this case, a second, separate oil supply conduit that extends from the cup-shaped jacket to the piston and to the clearance compensation element would be required in combination with separate control conduits within the cylinder head.
A further drawback of the tappet known from the above-mentioned publication is its lack of disclosing for both locking elements a limitation of axial displacement or a safety mechanism to safeguard a loss thereof. Moreover, as the base is of flat configuration, the external cam has only a limited support on the base for actuating the outer housing part. In order to ensure the area that is required during the migration of the cam on the base of the tappet, and to realize the desired valve lift diagrams, a base of cylindrical configuration in the camshaft direction would be desirable.
SUMMARY OF THE INVENTION
The invention is thus based upon the object to create a tappet of the above-stated type, obviating the aforestated drawbacks and effecting in particular a simple and reliable coupling mechanism with joint control of the hydraulic element at the same time, while assuring the required valve lift diagrams.
In accordance with the invention, this object is attained by providing the circular base section and the circular ring shaped base section with radially oriented bores that are in alignment in a base circle phase of the cams and receive as coupling means at least one piston which is shiftable by a pressure medium in opposition to a spring force, and by configuring the piston for displacement in radial direction in the event of engagement of both units such that it bridges with its outer peripheral surface an annular partition plane which is defined between both units and extends in axial direction. This configuration effects a simple coupling mechanism for both elements. As the bases of these elements are of cylindrical configuration as viewed in direction of the camshaft, the desired valve lift diagrams are assured in a simple fashion because now the base exhibits the support surface required for the cams. The control and operation of the tappet should be effected in dependence of such operational conditions like engine speed, load and temperature. In the lower speed and load range, at least one intake valve is switched over to a valve lift diagram with small lift and small opening angle, or is completely out of action. Thus, the mixture formation and combustion is positively affected by the forming swirl in the combustion
REFERENCES:
patent: 5090364 (1992-02-01), McCarroll et al.
patent: 5287830 (1994-02-01), Dopson et al.
patent: 5361733 (1994-11-01), Spath et al.
Elendt Harald
Faria Christof
Fischer Gerald
Haas Michael
Maas Gerhard
Feiereisen Henry M.
INA Walzlager Schaeffler KG
Lo Weilun
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