Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1994-10-03
1995-12-12
Yuen, Henry C.
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, 464 2, 74568R, F01L 134
Patent
active
054740380
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for automatic angular adjustment between two shafts in driving relationship.
Camshafts used in internal combustion engines actuate the engine valves in keeping with the profile of their cams. Fixed valve timings constitute a compromise particularly with regard to requirements concerning rated output and torque. The use of phase shifting to optimize valve timings is known. In an internal combustion engine with double camshafts this means that the position of the camshaft for the inlet or the exhaust valves is displaced with respect to the crankshaft by a certain crank angle which results in a change in the valve lap of the inlet and exhaust valves.
A device for the angular adjustment of a camshaft is known from DE-A 39 29 621. A drive gear of this adjusting device is made in one piece with a hollow hub which is mounted for angular displacement with its outer periphery in an outer recess of the shaft. The hollow hub cooperates by means of a helical gearing with a coupling member which is rigidly connected via a guide member to the camshaft in an inner recess thereof. To obtain a relative angular displacement of the camshaft with respect to the drive gear, the coupling member is axially displaceable being connected by a coupling rod to a hydraulic piston. A cylinder which is releasably mounted in the cap serves as a guide for the piston. This cylinder which is arranged in a stepped bore comprises circumferentially spaced openings on its pressure and suction ends. The arrangement of the piston results in two differently dimensioned piston areas which give rise to different adjusting speeds of the piston under the same pressure and are particularly disadvantageous in rapid switching operations.
A valve control for inlet valves is known from the species defining document, DE-C 38 10 804, in which the inlet camshaft can be adjusted with the help of a phase transformer. An adjusting element is mounted for axial displacement and comprises an exclusively hydraulically actuatable piston which is associated with two working chambers and controlled by an adjusting piston of a directional control valve. This adjusting piston is displaced between two discrete end positions by a solenoid switch which is arranged on the produced longitudinal axis of the camshaft and therefore increases the axial design space requirement of the engine. A pressure medium can be applied to both ends of the piston of the adjusting element and is fed to the adjusting element through a partially bored-open camshaft. The adjusting element is arranged between the camshaft and the driving gear of the camshaft and comprises a helical internal gearing and a helical external gearing with identical but oppositely oriented helix angles cooperating with appropriate gearings on the camshaft and the driving gear of the camshaft. This construction, particularly the control valve, permits only a two-point adjustment of the inlet camshaft. The extra design space required due to the chosen arrangement of the solenoid is disadvantageous particularly when the engine is installed crosswise. Moreover, the supply of pressure medium through the camshaft necessitates a special structural configuration and mounting of the camshaft in order to avoid an influence on the strength of the camshaft and the lubrication at mounting parts.
A further device for the angular adjustment of a camshaft is known from EP-A 01 63 046 in which an arrangement for feeding a pressure medium to a hydraulic adjusting device is located in a camshaft in the mounting region thereof. The housing in which the camshaft is mounted comprises oil bores through which the hydraulic oil is transported in the radial direction in the mounting region of the camshaft and via peripheral grooves into the camshaft. The hydraulic oil is transferred through tap bores into axially extending bores of the camshaft and from there to the adjusting piston. This construction requires a special camshaft structure as also appropriate aligning measures for the pressure medium feeding arrang
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Golovatai-Schmidt Eduard
Weigmann Gerhard
INA Walzlager Schaeffler KG
Lo Weilun
Yuen Henry C.
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