Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1998-01-26
1999-03-09
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9019, 123198F, F01L 1300, F01L 114
Patent
active
058787054
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus for selective actuation of at least one gas exchange valve with a switchable cam follower which is operatively connected between at least one cam of a camshaft and the gas exchange valve, or with a support device for a cam follower, including at least two members which can be displaced relative to each other and coupled to one another, with the first member communicating with the cam of great lift in order to provide a great valve lift, wherein the cam follower or the support device includes a coupling element which can be moved in at least one displacement direction through hydraulic fluid for selectively connecting the two members such as to transmit the great cam lift to the gas exchange valve, and wherein at least one channel extends in the cam follower or the support device for supplying and draining the hydraulic fluid.
BACKGROUND OF THE INVENTION
An apparatus of this type is described, for example, in DE-A 42 06 166. There, the two members are coupled through pistons which are arranged along the circumference and which can be moved radially in the coupling direction from the outside towards the inside via hydraulic fluid in opposition to the biasing force of an annular spring. For decoupling, the annular spring moves the respective pistons radially outwardly, counteracting the hydraulic pressure behind an annular surface separating the two members. Disadvantageously, however, the apparatus described in the above referenced patent document exhibits problems in conjunction with switching times, in particular at low temperatures when the hydraulic fluid has a high viscosity. If the internal combustion engine is started at relatively low ambient temperatures, the viscosity of the hydraulic fluid can be so high that the spring unit cannot move the piston into the decoupled position during the time available for the decoupling process (base circle). Such switching problems occur in particular when the internal combustion engine is operated not only at low ambient temperatures, but-after starting-also in a speed range above the idle speed, for example at partial load or even full load.
OBJECT OF THE INVENTION
It is therefore an object of the invention to provide an apparatus of the afore-stated type which obviates these drawbacks and which employs simple measures to eliminate problems associated with the switching times, in particular at a low ambient temperature of the internal combustion engine when the hydraulic fluid is highly viscous.
SUMMARY OF THE INVENTION
The object of the invention is solved by associating with the return channel for the hydraulic fluid an orifice plate or an orifice plate-like bore. In another embodiment of the invention, the orifice plate has the form of a standard orifice plate or standard-type orifice plate with sharp edges, wherein the flanks of the orifice plate enclose an angle of about 60.degree. to 90.degree. and open in the reverse flow direction. In another preferred embodiment, the return channel for the hydraulic fluid can include a relief channel for at least a portion of the returning hydraulic fluid, wherein the orifice plate is disposed in the relief channel. By using this type of orifice plate which is described, for example, in German Industrial Standard DIN 1952, the volume flow rate of the hydraulic fluid becomes essentially independent of the viscosity. In other words, the invention eliminates the afore-described timing problems which occur especially at low ambient temperatures of the internal combustion engine. With the application of an orifice plate of this type in the reverse flow direction of the hydraulic fluid, the quantity of returning hydraulic fluid per unit of time, i.e. the flow rate, is expected to be constant over all ranges in temperature and viscosity. This problem is discussed extensively in the published lecture notes from the lecture entitled "Fundamentals of Oil Hydraulics" by Prof. Dr. Ing. W. Backe, 6.sup.th edition 1986, RWTH Aachen (pages 2-40 ff. and 2-14 and fol
REFERENCES:
patent: 4741298 (1988-05-01), Rhoads
patent: 5090364 (1992-02-01), McCarroll et al.
patent: 5158048 (1992-10-01), Siemens
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patent: 5345904 (1994-09-01), Dopson et al.
Der Hydraulik-Trainer, Lehr-und Informationsbuch uber die Hydraulik, 2 Ed. , 11.80, G.L. Rexroth GmbH, Lohr A. Main, 1978, p. 129-135.
Backe, W.: Grundlagen der Olhydraulik, 5. Ed., RWTH, Aachen, 1986, p. 2-39 to 2-41.
Feiereisen Henry M.
Ina Walzlager Schaeffler OHG
Lo Weilun
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