Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1996-10-01
1998-11-10
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9048, F01L 1300
Patent
active
058328840
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a device for operating a valve drive of an internal combustion engine comprising a switching mechanism for switching to different valve lift curves of a gas exchange valve. The invention further concerns a method of operating a valve drive of an internal combustion engine.
Such switching mechanisms effect a reduction of friction in the valve drive especially at low to medium rotation speeds of the internal combustion engine by actuating only one of preferably two gas exchange valves in opening direction. However, since the switched-off element executes an idle stroke against the force of a spring, unnecessary friction still occurs on this element. In addition, the element in question is retained by the force of this spring on the control cam concerned. If, now, a switching-off is required at high rotation speeds, the spring used must be very strong but the limited design space restricts this possibility so that the maximum rotation speed of the internal combustion engine has also to be limited. Moreover, if the moment of time of re-switching is unfavorable, increasing noise and wear problems can occur.
SUMMARY OF THE INVENTION
The object of the invention is therefore to create a device and a method of the type initially cited avoiding the mentioned drawbacks while particularly enabling a disconnection of the cam follower from the cam with low friction even at medium to high rotation speeds and permitting a re-connection of the cam follower with low noise and wear.
The invention achieves this object according to the present invention by the fact that the switching mechanism is an integral part of, or supports a cam follower arranged in driving relationship between a camshaft and the gas exchange valve, the switching mechanism comprises a hollow cylindrical housing in whose interior extends an axially displaceable inner element which can be coupled thereto, the housing and the inner element each comprising at least one first radial or tangential bore or recess aligned in the base circle phase of the cam of the camshaft, said bore or recess houses at least one piston or pin which is displaceable in bore direction and serves as a coupling means which effects coupling by bridging an annular gap formed between the housing and the inner element, at least one further radial or tangential bore or recess aligned in a phase of maximum cam lift is arranged in the housing and in a surrounding structure in form of an outer casing, and at least one further coupling element displaceable in bore direction is arranged in said further bore or recess and, to effect an uncoupling of the cam follower from the cam, said further coupling element is displaced so as to bridge an annular gap formed between the housing and the surrounding structure while extending simultaneously into both bores or recesses. According to an alternative solution, the housing or the inner element comprises at least one further bore or recess axially spaced from the first bore or recess and into which, for disconnecting the finger lever from the cam, the piston or pin arranged in the facing component (inner element or housing) is displaceable in the phase of maximum cam lift so as to bridge an annular gap formed between the housing and the inner element.
The measures of the invention make it possible for the support element concerned to be uncoupled from the lifting contour of the control cam when a disconnection of the cam follower is desired. At the same time, the cam follower is out of driving relationship to the control cam so that the aforesaid detrimental friction losses are eliminated because the cam follower is thus only temporarily pressed against the control cam in case of uncoupling. The aforementioned further coupling element keeps the housing and the cam follower, which is force-locked on the housing, out of contact with the lifting movement of the control cam after the housing of the switching mechanism has executed an idle stroke. The disadvantageous idle stroke of the housing relative
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Haas Michael
Speil Walter
Feiereisen Henry M.
Ina Walzlager Schaeffler OHG
Lo Weilun
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