Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-11-12
2000-05-09
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9039, 123198F, F01L 1300
Patent
active
060588950
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
For modern reciprocating internal combustion engines with conventional valve drives for actuating the valves via a camshaft and a corresponding lever arrangement, it is desirable to change the valve lift in accordance with the values predetermined in a performance diagram in order to optimize the combustion.
SUMMARY OF THE INVENTION
In order to solve this problem, a means for actuating valves on a reciprocating internal combustion engine is suggested in accordance with the invention, which comprises at least one camshaft, wherein respectively one cam acts upon a lever arrangement actuating at least one valve and having two pivotally mounted levers, of which one lever is connected to the cam and the other lever is connected to the valve to be actuated, wherein the separate levers are connected to each other via an adjustment means, which can be used to adjust an idle stroke between cam lever and valve lever. This makes it possible to vary the start and the end of the valve lift as well as the extent of the valve lift itself through a specific change in the idle stroke position relative to each other of the two levers. Depending on the operation, this can be done, for example, in dependence on a predetermined performance diagram for an electronic motor control device. The lever arrangement can be designed as valve rocker as well as cam lever arrangement.
The embodiment of the invention provides that the cam lever and the valve lever are positioned on a control shaft, which is positioned such that it can be turned back and forth relative to the lever arrangement, is designed to actuate the adjustment means and is connected to an actuator that can be triggered. This arrangement has the advantage that the positioning of the lever arrangement simultaneously functions as device for actuating the adjustment means, wherein the necessary actuator can be designed to be activated mechanically, hydraulically or even electromagnetically.
In this connection, a useful embodiment provides that the cam lever is connected to a spring-mounted support element that is effective against the cam. The arrangement of a spring-mounted support element on the one hand has the effect that the cam lever always fits against the cam on the cam side, so that with a reduced valve lift that is predetermined by the adjustment means, the cam lever "breathes" over a section of the lift predetermined by the cam geometry, meaning that it has no effect on the valve lever.
For another embodiment of the invention, it is provided that the adjustment means is formed by a pressure cylinder arranged in one of the levers, and by a transmission element moving as a piston within the pressure cylinder, which supports itself with its free end on the other lever, and that the pressure cylinder has a bypass channel, which can be connected via a cross bore in the control shaft to a pressure medium channel in the control shaft by turning the control shaft. This design for the adjustment means has the advantage that the contact between the transmission element and the lever that fits against it is always ensured via the pressure medium. In the most simple form, the idle stroke can be predetermined through the position of the cross bore in the control shaft with respect to the feed channel for the pressure cylinder. With a corresponding position of the cross bore, the relative motion of the lever comprising the pressure cylinder closes the connection between cross bore and feed channel with the slider, so that the residual volume of the incompressible pressure medium, together with the transmission element, acts like a rigid body, thereby transmitting the forces between cam and valve spring in full. It is possible in this case as well to keep the cam lever in continuous contact with the cam via he pull-back spring on the cam lever, so that the cam lever "breathe" over a corresponding portion of the total lift, depending on the position of the cross bore to the feed channel of the pressure cylinder, until th
REFERENCES:
patent: 5113813 (1992-05-01), Rosa
patent: 5544628 (1996-08-01), Voigt
patent: 5609133 (1997-03-01), Hakansson
FEV Motorentechnik GmbH & Co.
Lo Weilun
Spencer George H.
Wells Ashley J.
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