Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1998-04-03
1999-10-26
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, F01L 1344
Patent
active
059709308
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a device for varying the opening and closing times of gas exchange valves of an internal combustion engine, which device is disposed within a control gear of at least one inlet or exhaust camshaft mounted in a cylinder head, with the device being preferably arranged on a drive pinion which is in driving relationship with the camshaft, wherein the device includes an adjusting piston which is axially displaceable by hydraulic medium and possesses two preferably oppositely oriented helical gear sections, the first of which sections cooperates with a complementary gearing of a drive unit which is rotationally fixed to the drive pinion, and the second section cooperates with a complementary gearing of a driven unit which is rotationally fixed to the camshaft, the drive and the driven units comprising opposing end faces.
BACKGROUND OF THE INVENTION
A device of this type is known from DE-PS 29 09 803. With a device of this type, the problem arises on starting of the internal combustion engine, that the adjusting piston concerned moves at a high speed into a position of maximum displacement in which its repeated abutting is accompanied by a considerable amount of noise. This is due to the fact that when the engine has been turned off, the hydraulic medium contained in the device gradually escapes therefrom so that the adjusting piston is no longer sufficiently supported hydraulically although, as a rule, a certain residual amount of hydraulic medium is still present. Due to the torsional vibrations of the camshaft, the adjusting piston, which is now no longer hydraulically supported, is displaced into an end position on re-starting of the engine, with the already mentioned considerable noise generation. This state prevails during the period of time between the ignition of the engine and the filling of the pressure chambers, that is to say, for a few seconds after the engine has been started.
OBJECT OF THE INVENTION
The object of the invention is therefore to create a device of the aforesaid type in which the mentioned drawbacks are eliminated and the indicated start rattling is avoided, particularly with the use of simple means i.e., with only minor constructional measures.
SUMMARY OF THE INVENTION
The invention achieves the above object by providing at least one coupling means arranged preferably parallel to the longitudinal axis of the camshaft extends in a first lodging in one of the two units in the region of the opposing end faces, by providing in the other of the two units a further lodging into which the coupling means can be partly displaced in one relative rotational position of the units by the force of a spring means, wherein the coupling means can be displaced in uncoupling direction into the first lodging with servo assistance such as by hydraulic medium. Advantageous embodiments are the subject matter of the dependent Claims.
The means provided by the invention preclude the rattling noises encountered in the prior art which are caused by a high frequency abutment of the adjusting piston against one of its end positions. As soon as the device has run empty of hydraulic medium to the largest possible extent after the internal combustion engine has been put out of action, the hydraulic support of the adjusting piston is practically non-existent. A compression spring displaces the adjusting piston into the desired start or emergency running position. As a rule, this position in the case of an intake adjuster would be the retard position, and in the case of an exhaust adjuster, the advance position. In an intake adjuster, this movement is assisted by the acting drag and frictional torques of the camshaft. The invention provides that as soon as this position has been reached, the drive and the driven unit of the device are positively coupled to each other. This measure prevents a further axial movement of the adjusting piston until sufficient hydraulic medium pressure has been built up in the device, which pressure disengages a coupling means which is
REFERENCES:
patent: 5080052 (1992-01-01), Hotta et al.
patent: 5301639 (1994-04-01), Satou
Goppelt Dieter
Hess Stefan
Scheidt Martin
Feiereisen Henry M.
Ina Walzlager Schaeffler OHG
Lo Weilun
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