Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1999-01-26
2000-08-22
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, 74568R, 464 2, 464161, F01L 1344
Patent
active
061055441
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus for changing the opening and closing times of gas exchange valves of an internal combustion engine.
BACKGROUND OF THE INVENTION
An apparatus of this type is known from German Pat. No. DE-PS 29 09 803. After start of the internal combustion engine, the apparatus of this type has the problem that the respective adjusting piston travels at high speed into a maximum adjustment position and repeatedly impacts there at significant generation of noise. The reason for this is the fact that after shutdown of the internal combustion engine, hydraulic fluid residing in the apparatus gradually escapes from there so that the adjusting piston is no longer sufficiently supported, whereby, normally, a certain residual volume of hydraulic fluid is retained. As a consequence of the irregular rotation of the camshaft, the adjusting piston is shifted, after re-starting the internal combustion engine, into an end position under the mentioned significant noise development, because the adjusting piston is no longer hydraulically supported. This condition is observed during the period between ignition of the internal combustion engine and charging of the pressure compartments, i.e. few seconds after start of the engine.
SUMMARY OF THE INVENTION
It is thus an object of the invention, to provide an apparatus of the afore-mentioned type, obviating the pointed out drawbacks and in particular eliminating with simple means, i.e. with little constructive means, the described rattling at start and an oscillation of the angle of adjustment between camshaft and crankshaft, while creating at the same time a possibility for displacement of the apparatus into its starting position even when the adjusting piston is no longer hydraulically supported.
SUMMARY OF THE INVENTION
This object is attained in accordance with the invention by providing at least one locking means which, on the one hand, substantially bars the undesired adjusting direction when the pressure of hydraulic fluid in the respective pressure compartment falls below a required level for realizing a displacement of the adjusting piston into the desired preferred position, and, on the other hand, realizes a displacement into the preferred position via an auxiliary energy such as the component of the varying moments of the camshaft, acting in this direction.
Through the provision of locking means according to the invention a form-fitting connection between drive element and driven element of the apparatus is realized while the apparatus is largely in a hydraulic-fluid-free state. Thus, disadvantageous rattling noises encountered in the state of art as a consequence of high-frequency impacts of the adjusting piston in its one end position can thus be eliminated. On the other hand, the invention proposes that, in the event the adjusting piston does not occupy its desired starting position before re-ignition of the internal combustion engine, the adjusting piston is brought into this starting position via an auxiliary energy, such as the occurring varying moments of the camshaft. At the same time, a shift of the adjusting piston into its undesired starting position is substantially prevented by the invention.
Although immediately before shutdown of the internal combustion engine, the adjusting piston should be brought tentatively into its desired starting position through hydraulic fluid acting on the respective pressure compartment, there are, however, operational conditions of the internal combustion engine conceivable during which this state cannot be realized. For example, this would be the case when the internal combustion engine is merely operated over an extremely short period or inadvertently shuts down ("stalls"). The locking means according to the invention, for example formed as freewheel means or step-like or saw-tooth-like locking mechanism, thus preventing immediately after operating the internal combustion engine a shift of the adjusting piston into its undesired impact position. At the same time, th
REFERENCES:
patent: 5558053 (1996-09-01), Tortul
patent: 5823152 (1998-10-01), Ushida
Auchter Jochen
Kohrs Mike
Strauss Andreas
Feiereisen Henry M.
Ina Walzlager Schaeffler OHG
Lo Weilun
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