Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-08-18
1999-04-27
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, 74568R, 464 2, 464160, F01L 1344
Patent
active
058968369
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention concerns a device arranged on an internal combustion piston engine for adjusting positions of rotation of at least one camshaft relative to a crankshaft, said device comprising a hydraulic cylinder comprising a piston and a first feed duct, a hydraulic valve arrangement with which a hydraulic connection can be established between the first feed duct and a first outlet duct being disposed between said hydraulic cylinder and a hydraulic pump.
A device of the pre-cited type is known, for example, from WO-A-93/07362. Linear adjusting movements of the piston are converted by means of an adjusting member into rotary movements of a drive member relative to the camshaft. Rotations of the crankshaft are transmitted to the camshaft by the drive member. The drive member is normally a pinion driven by the crankshaft with the help of a chain. The adjusting member is arranged between this pinion and the camshaft. The adjusting member which is constituted, for example, by the piston and arranged concentric to the pinion and the camshaft, comprises a helical gearing and a spur gearing, said gearings cooperating with corresponding gearings associated to the camshaft and the pinion. On actuation of the hydraulic cylinder, the adjusting member is displaced axially relative to the pinion and the camshaft, and due to the helical gearing, a rotation of the camshaft takes place relative to the pinion.
In the prior art device, the first outlet duct opens into an oil pan so that fluid from the cylinder can flow into the oil pan. As described more closely below, the use of this prior art device can lead to the occurrence of rattling noises during the starting of the internal combustion piston engine. The hydraulic pump is normally driven by the internal combustion piston engine which cannot build up pressure during starting. If the engine is started after a long standstill, such a quantity of the fluid stored in the cylinder has leaked out that compressible gas cushions are formed in the cylinder. As a result, a linear movement of the piston guided in the cylinder is possible even when the pressure chambers of the cylinder are closed. Due to the above-mentioned helical gears, the alternating torques transmitted from the camshaft to the adjusting member exert axial forces on the adjusting member. Due to the compressible gas cushions, these axial forces cause oscillatory movements of the piston which migrates further towards one end of the cylinder and finally strikes against this end thus causing rattling noises by its oscillation.
It is an object of the invention to assure by simple means that such rattling nosies cannot occur.
The invention achieves the above object in that the first outlet duct opens into a fluid reservoir below the fluid level therein. In the one direction of movement of the oscillating piston, the gas eventually enclosed in the cylinder is displaced and pumped into the fluid reservoir from which it can escape. In the other direction of movement of the oscillating piston, fluid is sucked into the cylinder from the fluid reservoir. This prevents the piston from striking against an end of the cylinder. The undesired oscillatory movements of the piston are thus exploited for producing a pumping effect. Advantageously, the volumes of fluid or gas displaced between the cylinder and the fluid reservoir due to the piston displacements are larger than the capacity of the ducts between the cylinder and the fluid reservoir.
In an advantageous development of the invention, the first feed duct is arranged on one side of the piston and a second feed duct is arranged on the other side of the piston on the cylinder. Such double-action cylinders assure a reliable control of the adjusting movements of the piston.
In a particularly advantageous embodiment, the hydraulic valve arrangement is constituted by a 4/3 directional control valve. In a first operating position of the valve, hydraulic connection is established between the first feed duct and the fluid reservoir, and between the second feed duct an
REFERENCES:
patent: 4452188 (1984-06-01), Kosuda et al.
patent: 5333577 (1994-08-01), Shinojima
patent: 5421294 (1995-06-01), Ruoff et al.
patent: 5509383 (1996-04-01), Kahrs et al.
Golovatal-Schmidt Eduard
Scheidt Martin
Strauss Andreas
INA Walzlager Schaeffler KG
Lo Weilun
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